Wafer double-side polishing apparatus and double-side polishing method

ABSTRACT

The present invention provides a wafer double-side polishing apparatus comprising at least a carrier plate having wafer holding holes; upper and lower turn tables to which polishing pads are attached; and a slurry supply means; with wafers held in the wafer holding holes, the carrier plate being moved between the upper and lower turn tables while supplying slurry, to simultaneously polish both front and back surfaces of wafers, wherein a PCD of upper turn table load supporting points that is a diameter of a circle joining load supporting points of the upper turn table coincides with a PCD of centers of the wafer holding holes on the carrier plate that is a diameter of a circle joining each center of the wafer holding holes on the carrier plate. Thereby, there can be provided a wafer double-side polishing apparatus and method in which it is possible to control wafer shape by deforming turn tables with excellent responsiveness, and to polish the wafers stably with high precision without deteriorating wafer shape.

TECHNICAL FIELD

The present invention relates generally to a polishing apparatus and apolishing method capable of maintaining time-varying wafer qualitystably during wafer polishing using a double-side polishing apparatus,and more particularly to a wafer double-side polishing apparatus and adouble-side polishing method for polishing wafers while controllingwafer shape by controlling at least an upper turn table shape of thedouble-side polishing apparatus that polishes both front and backsurfaces of wafers at the same time.

BACKGROUND ART

A silicon wafer manufacturing method will be described as an example ofconventional wafer manufacturing method. Silicon single crystal ingotsare first grown by the Czochralski method (CZ method), etc., and slicedinto silicon wafers. Then those silicon wafers are subjected tochamfering, lapping and etching steps in succession, after which thewafers undergo a polishing step where at least the wafer main surface ismirror-polished.

In the wafer polishing step, a double-side polishing apparatus is usedoccasionally when both front and back surfaces of silicon wafers arepolished. As the double-side polishing apparatus, a so-called four-waydouble-side polishing apparatus is normally employed that has aplanetary gear construction in which carrier plates for holding wafersare arranged between a sun gear provided at the center portion and aninternal gear provided at the perimeter portion.

The four-way double-side polishing apparatus can simultaneously polishboth front and back surfaces of silicon wafers by inserting siliconwafers into and holding them in a plurality of carrier plates on whichwafer holding holes are formed, pressing upper and lower turn tables, inwhich polishing pads are attached to wafer-facing surfaces, againstfront and back surfaces of each wafer and rotating the turn tables inrelative directions while supplying polishing slurry from above the heldsilicon wafers and by concurrently rotating and revolving the carrierplates using the sun and internal gears.

A double-side polishing apparatus as described in Japanese PatentLaid-open (Kokai) Publication No. 10-202511 is among other known formsof double-side polishing apparatuses. FIG. 5 illustrates a schematicsectional view of the double-side polishing apparatus. A double-sidepolishing apparatus 41 comprises a carrier plate 46 with a plurality ofwafer holding holes in which silicon wafers 44 are held, upper and lowerturn tables 42 and 43 which are arranged above and below the carrierplate 46 and to whose wafer-facing surfaces polishing pads 45 areattached for simultaneously polishing both front and back surfaces ofthe silicon wafers 44 and carrier motion means (not shown) for movingthe carrier plate 46 sandwiched between the upper and lower turn table42 and 43 within a plane parallel to the front surface of the carrierplate 46. The upper turn table 42 is provided with a cylinder 47 forapplying rotation and polishing loads, a housing 48 for transmittingthose loads to the upper turn table 42 and fixing means 49 such as boltsfor fixing the housing 48 and the upper turn table 42. On the otherhand, the lower turn table 43 is provided with the cylinder 47 forimparting rotation from a motor and a speed reducer (not shown) to thelower turn table 43 and a thrust bearing 50 that supports the load ofthe turn tables.

In such the double-side polishing apparatus 41, the carrier plate 46,sandwiched between the upper and lower turn tables 42 and 43, is causedto make a circular motion not accompanied by its rotation by the carriermotion means (not shown) via a carrier holder 51, that is, a type ofswinging motion in which the carrier plate 46 circles without rotatingwhile remaining eccentric by a given distance from the rotational axisof the upper and lower turn tables 42 and 43. At this time, the siliconwafers 44 are held in the wafer holding holes of the carrier plate 46 soas to be rotatable, allowing the silicon wafers 44 to turn together(rotate) in the direction of rotation of the faster rotating turn tableas a result of rotation of the upper and lower turn tables at differentspeeds or in different directions on the rotational axis.

Therefore, when both front and back surfaces of silicon wafers arepolished, it is possible to simultaneously and uniformly polish bothfront and back surfaces of silicon wafers by inserting the siliconwafers into respective wafer holding holes on the carrier plate, holdingthe silicon wafers therein and causing the carrier plate to make acircular motion not accompanied by its rotation while causing the wafersthemselves to rotate in the wafer holding holes by rotating the upperand lower turn tables at different speeds or in different directions,with slurry containing polishing abrasive grain supplied to the siliconwafers. Double-side polishing apparatuses in such a form have latelycome into frequent use with recent increase in wafer diameter since theapparatuses are capable of double-side polishing of large-sized waferswith ease.

However, if a plurality of batches of wafers are polished repeatedlyusing a four-way double-side polishing apparatus as described above ordouble-side polishing apparatus that polish wafers by causing thecarrier plate to make a circular motion not accompanied by its rotation,the polishing ability and other factors of polishing pads attached tothe upper and lower turn tables change over time due to polishing pads'life, clogging and other factors. For this reason, polishing of aplurality of batches of wafers without replacement of the polishing padshas given rise to change in polished wafer shape over time with morepolished batches, resulting in wafer shape differences between batchesand problems that it is impossible to maintain wafer quality stably.

To solve the problems, wafers have traditionally been polished bychanging various polishing conditions according to changes in polishingability of the polishing pads and other factors over time, therebycontrolling change in wafer shape over time. For instance, there is amethod for controlling wafer shape in which the turn table shape itselfis changed by changing conditions such as turn table temperature.

Although turn tables thought to be preferred for use in a double-sidepolishing apparatus are those that do not deform during wafer polishing,if such turn tables not deforming during wafer polishing are used, itwill be difficult to ensure a fit between wafers and turn tables undervarying polishing conditions. Moreover, it will be impossible to controlwafer shape in response to changes in polishing ability and otherfactors of polishing pads over time.

To avoid such difficulties associated with wafer shape control, turntables are generally made of a material that deforms to a certain extentand particularly under varying temperatures, thus allowing wafer shapecontrol by flowing cooling water, etc., through the turn tables andchanging their temperature to vary the shape of the turn tables.

However, despite an attempt to control wafer shape by flowing coolingwater, etc., through the turn tables and changing their temperature, theresponsiveness of turn table deformation to varying turn tabletemperature (linearly relative to change in turn table temperature andthe like) in conventional double-side polishing was poor, making itimpossible to ensure high precision in the turn table shape control.Particularly if polishing conditions and the like are substantiallychanged during wafer polishing, there was caused a problem that it hasbeen impossible to control the turn tables into a desired shape throughthe temperature control in the turn tables alone. When a plurality ofbatches of wafers are polished repeatedly, it has been difficult tocontrol the turn table shape as desired with increasing number of waferbatches due to poor responsiveness of turn table deformation, making itimpossible to control batch-by-batch wafer shape stably and with highprecision. In particular, repeated polishing of a plurality of batchesof large-sized wafers such as 300 mm-diameter wafers has often led to aconvex wafer shape, thus exhibiting remarkably deteriation of a wafershape such that flatness of GBIR (Global Back Ideal Range), etc. isdeteriorated. In other words, conventional turn table temperaturecontrol alone has failed to sufficiently control time-varying wafershape.

DISCLOSURE OF THE INVENTION

The present invention was conceived in light of the abovementionedproblem. It is a first object of the present invention to provide awafer double-side polishing apparatus and method in which it is possibleto control wafer shape by deforming turn tables with excellentresponsiveness in response to changes over time in polishing ability andother factors of polishing pads attributed to their life, clogging orother cause, and to polish the wafers stably with high precision withoutdeteriorating wafer shape even in repeated polishing of a plurality ofbatches of wafers. Further, it is a second object of the presentinvention to provide a wafer double-side polishing apparatus and methodthat ensure good precision in wafer shape control by controlling theturn table shape with high precision and that ensure stable polishingwith high precision even during repeated polishing of a plurality ofbatches of wafers.

To accomplish the first object, according to the present invention,there is provided a wafer double-side polishing apparatus comprising atleast a carrier plate having wafer holding holes; upper and lower turntables to which polishing pads are attached; and a slurry supply means;with wafers held in the wafer holding holes, the carrier plate beingmoved between the upper and lower turn tables while supplying slurry, tosimultaneously polish both front and back surfaces of wafers, wherein aPCD of upper turn table load supporting points that is a diameter of acircle joining load supporting points of the upper turn table coincideswith a PCD of centers of the wafer holding holes on the carrier platethat is a diameter of a circle joining the each center of the waferholding holes on the carrier plate.

Thus, by using such a double-side polishing apparatus comprising atleast a carrier plate, upper and lower turn tables and a slurry supplymeans, with the carrier plate being moved between the upper and thelower turn tables to polish wafers, wherein a PCD (Pitch CircleDiameter) of upper turn table load supporting points that is a diameterof a circle (hereafter sometimes referred to as “pitch circle”) joiningload supporting points of the upper turn table coincides with a PCD ofcenters of the wafer holding holes on the carrier plate that is adiameter of a circle joining each center of wafer holding holes on thecarrier plate, it is possible to provide turn table deformation withimproved responsiveness to changes in polishing conditions during waferpolishing, thus facilitating the turn table shape control. Thereby,there can be provided the apparatus that allows the turn table shapecontrol by properly changing polishing conditions in accordance withchanges in polishing ability and other factors of polishing pads overtime during repeated polishing of a plurality of batches of wafers, andthat is capable of polishing with controlling easily batch-by-batchwafer shape without deteriorating wafer shape.

At this time, it is preferred that the motion of the carrier plate be acircular motion not accompanied by the rotation of the carrier plate.

Thus, if the carrier plate motion is a circular motion not accompaniedby the rotation of the carrier plate, that is, a swinging motion inwhich the carrier plate circles without rotating while remainingeccentric by a given distance from the rotational axis of the upper andlower turn tables, all points on the carrier plate trace a smallcircular trajectory of the same size, allowing uniform polishing acrossboth front and back surfaces of wafers.

Further, according to the present invention, there is provided a waferdouble-side polishing apparatus comprising at least a plurality ofcarrier plates each having wafer holding holes; sun and internal gearsfor rotating and revolving the carrier plates; upper and lower turntables to which polishing pads are attached; and a slurry supply means;with wafers held in the wafer holding holes, the plurality of carrierplates being rotated and revolved between the upper and lower turntables while supplying slurry, to simultaneously polish both front andback surfaces of wafers, wherein a PCD of upper turn table loadsupporting points that is a diameter of a circle joining load supportingpoints of the upper turn table coincides with a PCD of carrier platecenters that is a diameter of a circle joining the centers of theplurality of carrier plates.

Thus, by using such a double-side polishing apparatus comprising atleast carrier plates, sun and internal gears, upper and lower turntables and a slurry supply means, with the carrier plates being rotatedand revolved between the upper and the lower turn tables to polishwafers, wherein a PCD of upper turn table load supporting points that isa diameter of a circle joining load supporting points of the upper turntable coincides with a PCD of carrier plate centers that is a diameterof a circle joining the centers of the plurality of carrier plates, itis possible to provide turn table deformation with improvedresponsiveness to changes in polishing conditions during waferpolishing, thus facilitating the turn table shape control. This allowsthe turn table shape control by properly changing polishing conditionsin accordance with changes in polishing ability and other factors ofpolishing pads over time during repeated polishing of a plurality ofbatches of wafers, and it is possible to polish with easily controllingbatch-by-batch wafer shape without deteriorating wafer shape.

At this time, it is preferred that a PCD of lower turn table loadsupporting points that is a diameter of a circle joining load supportingpoints of the lower turn table coincide with the PCD of the upper turntable load supporting points.

Thus, if, in a double-side polishing apparatus, a PCD of lower turntable load supporting points that is a diameter of a circle joining loadsupporting points of the lower turn table coincides with the PCD ofupper turn table load supporting points, it is possible to providefurther improved responsiveness to the turn table shape control,allowing batch-by-batch wafer shape control with high precision evenduring polishing of a plurality of batches of wafers.

A wafer double-side polishing method in accordance with the presentinvention is a wafer double-side polishing method comprising holdingwafers on a carrier plate on which are formed wafer holding holes forholding wafers; and, while supplying slurry, moving the carrier platebetween upper and lower turn tables to which polishing pads areattached, to simultaneously polish both front and back surfaces of thewafers, wherein the wafers are polished with causing a PCD of upper turntable load supporting points that is a diameter of a circle joining loadsupporting points of the upper turn table and a PCD of wafer centersthat is a diameter of a circle joining centers of the wafers held by thecarrier plate to coincide with each other.

In the double-side polishing method for simultaneously polishing bothfront and back surfaces of wafers as described above, by polishing thewafers with causing a PCD of upper turn table load supporting pointsthat is a diameter of a circle joining the load supporting points of theupper turn table and a PCD of wafer centers that is a diameter of acircle joining centers of the wafers held by the carrier plate tocoincide with each other, it is possible to easily control the turntable shape with excellent responsiveness. This allows precise controlin the turn table shape in accordance with change in wafer shape overtime, thus enabling stable polishing while maintaining wafer shape withgood precision even during repeated polishing of a plurality of batchesof wafers.

At this time, it is preferred that the motion of the carrier plate be acircular motion not accompanied by the rotation of the carrier plate.

Thus, by ensuring that the carrier plate motion is a circular motion notaccompanied by the rotation of the carrier plate, it is possible toconduct uniform polishing across both front and back surfaces of wafersheld by the carrier plate.

Further, according to the present invention, there is provided a waferdouble-side polishing method comprising holding wafers on a plurality ofcarrier plates each having thereon formed holding holes for holdingwafers; and, while supplying slurry, rotating and revolving theplurality of carrier plates using sun and internal gears between upperand lower turn tables to which polishing pads are attached, tosimultaneously polish both front and back surfaces of the wafers,wherein the wafers are polished with causing a PCD of upper turn tableload supporting points that is a diameter of a circle joining loadsupporting points of the upper turn table and a PCD of carrier platecenters that is a diameter of a circle joining centers of the pluralityof carrier plates to coincide with each other.

In a double-side polishing method for simultaneously polishing bothfront and back surfaces of wafers as described above, by polishingwafers with causing a PCD of upper turn table load supporting pointsthat is a diameter of a circle joining the load supporting points of theupper turn table and a PCD of carrier plate centers that is a diameterof a circle joining centers of the plurality of carrier plates tocoincide with each other, it is possible to easily control the turntable shape with excellent responsiveness. This allows precise controlin the turn table shape in accordance with change in wafer shape overtime, thus enabling stable polishing while maintaining wafer shape withgood precision even during repeated polishing of a plurality of batchesof wafers.

At this time, it is preferred that a PCD of lower turn table loadsupporting points that is a diameter of a circle joining load supportingpoints of the lower turn table be caused to coincide with the PCD of theupper turn table load supporting points.

Thus, by causing a PCD of lower turn table load supporting points thatis a diameter of a circle joining load supporting points of the lowerturn table to coincide with the PCD of the upper turn table loadsupporting points, it is possible to provide the turn table shapecontrol with further improved responsiveness, thus allowing reliablesuppression in batch-by-batch wafer shape change even during polishingof a plurality of batches of wafers.

Further at this time, it is preferred that during the wafer polishing,the wafers be polished while controlling polishing conditions and thatthe polishing conditions be controlled by controlling the upper and/orlower turn table temperature.

Thus, by polishing wafers while controlling the polishing conditions andpreferably the upper and/or lower turn table temperature during thewafer polishing, it is possible to control the turn table shape withexcellent responsiveness even during repeated polishing of a pluralityof batches of wafers. This allows polishing of a plurality of batches ofwafers without deteriorating wafer shape, thus making it possible tomaintain polished batch-by-batch wafer shape stably with good precision.

To accomplish the second object, according to the present invention,there is provided a wafer double-side polishing apparatus comprising atleast a carrier plate having wafer holding holes; upper and lower turntables to which polishing pads are attached; and a slurry supply means;with wafers held in the wafer holding holes, the carrier plate beingmoved between the upper and lower turn tables while supplying slurry, tosimultaneously polish both front and back surfaces of wafers, whereinshape adjustment means are disposed at load supporting point portions ofthe upper turn table.

Thus, by using such a double-side polishing apparatus comprising atleast a carrier plate, upper and lower turn tables and a slurry supplymeans, with the carrier plate being moved between the upper and thelower turn tables to polish both front and back surfaces of wafers,wherein shape adjustment means are disposed at load supporting pointportions of the upper turn table, it is possible to forcibly deform theupper turn table shape with the shape adjustment means, allowing properthe turn table shape control in accordance with changes in polishingability and other factors of polishing pads over time during waferpolishing. Thereby, there can be provided the apparatus that ensuresgood precision and stability in wafer shape during polishing, and thatis capable of polishing with easily controlling batch-by-batch wafershape without deteriorating wafer shape even during repeated polishingof a plurality of batches of wafers.

At this time, it is preferred that the motion of the carrier plate be acircular motion not accompanied by the rotation of the carrier plate.

Thus, if the carrier plate motion is a circular motion not accompaniedby the rotation of the carrier plate, that is, a swinging motion inwhich the carrier plate circles without rotating while remainingeccentric by a given distance from the rotational axis of the upper andlower turn tables, all points on the carrier plate trace a smallcircular trajectory of the same size, allowing uniform polishing acrossboth front and back surfaces of wafers.

Further at this time, it is preferred that a PCD of upper turn tableload supporting points that is a diameter of a circle joining the loadsupporting points of the upper turn table coincide with a PCD of centersof the wafer holding holes on the carrier plate that is a diameter of acircle joining each center of the wafer holding holes on the carrierplate.

Thus, by using such a double-side polishing apparatus in which a PCD(Pitch Circle Diameter) of upper turn table load supporting points thatis a diameter of a circle joining load supporting points of the upperturn table coincides with a PCD of centers of the wafer holding holes onthe carrier plate that is a diameter of a circle joining each center ofthe wafer holding holes on the carrier plate, it is possible to provideturn table deformation with further improved responsiveness toadjustment of the shape adjustment means, adjustment of slurry supplyamount, etc. thus allowing easy and precise control in the turn tableshape.

Further, according to the present invention, there is provided a waferdouble-side polishing apparatus, comprising at least a plurality ofcarrier plates each having wafer holding holes; sun and internal gearsfor rotating and revolving the carrier plates; upper and lower turntables to which polishing pads are attached; and slurry supply means;with wafers held in the wafer holding holes, the plurality of carrierplates being rotated and revolved between the upper and lower turntables while supplying slurry, to simultaneously polish both front andback surfaces of wafers, wherein shape adjustment means are disposed atload supporting point portions of the upper turn table.

Thus, by using such a double-side polishing apparatus comprising atleast carrier plates, sun and internal gears, upper and lower turntables and a slurry supply means, with the plurality of carrier platesbeing rotated and revolved between the upper and lower turn tables topolish both front and back surfaces of wafers, wherein shape adjustmentmeans are disposed at load supporting point portions of the upper turntable, it is possible to forcibly deform the upper turn table shape withthe shape adjustment means, allowing proper the turn table shape controlin accordance with changes in polishing ability and other factors ofpolishing pads over time during wafer polishing. Thereby, there can beprovided the apparatus that ensures good precision and stability inwafer shape during polishing, and that is capable of polishing witheasily controlling batch-by-batch wafer shape without deterioratingwafer shape even during repeated polishing of a plurality of batches ofwafers.

At this time, it is preferred that a PCD of upper turn table loadsupporting points that is a diameter of a circle joining load supportingpoints of the upper turn table coincide with a PCD of carrier platecenters that is a diameter of a circle joining centers of the pluralityof carrier plates.

Thus, by using such a double-side polishing apparatus in which a PCD ofupper turn table load supporting points that is a diameter of a circlejoining the load supporting points of the upper turn table coincideswith a PCD of carrier plate centers that is a diameter of a circlejoining centers of the plurality of carrier plates, it is possible toprovide turn table deformation with further improved responsiveness toadjustment of the shape adjustment means, adjustment of slurry supplyamount, etc. thus allowing easy and precise control in the turn tableshape.

Further, it is preferred that the shape adjustment means be micrometers.

Thus, if the shape adjustment means are micrometers, it is possible tomechanically press the upper turn table by a desired magnitude andforcibly deform the upper turn table through adjustment of themicrometers, allowing precise deformation of the table into a desiredshape.

It is also preferred that materials of the turn table be stainlesssteel.

Thus, if the turn table is made of stainless steel, it is possible toproperly deform the turn table, allowing easy deformation of the turntable with the shape adjustment means, etc.

A wafer double-side polishing method in accordance with the presentinvention is a wafer double-side polishing method comprising holdingwafers in wafer holding holes formed on a carrier plate; and whilesupplying slurry, moving the carrier plate between upper and lower turntables to which polishing pads are attached, to simultaneously polishboth front and back surfaces of the wafers, wherein the wafers arepolished while controlling the turn table shape by adjusting the slurrysupply amount.

In such a double-side polishing method for simultaneously polishing bothfront and back surfaces of wafers as described above, it is possible tocontrol polishing surface temperature by adjusting slurry supply amountduring polishing, thus allowing the turn table shape control withexcellent responsiveness. This ensures stable polishing withoutdeteriorating wafer shape.

At this time, it is preferred that the motion of the carrier plate be acircular motion not accompanied by the rotation of the carrier plate.

Thus, by ensuring that the carrier plate motion is a circular motion notaccompanied by the rotation of the carrier plate, it is possible toconduct uniform polishing across both front and back surfaces of wafersheld by the carrier plate.

Further, according to the present invention, there is provided a waferdouble-side polishing method comprising holding wafers on a plurality ofcarrier plates each having thereon formed holding holes for holdingwafers; and while supplying slurry, rotating and revolving the pluralityof carrier plates using sun and internal gears between upper and lowerturn tables to which polishing pads are attached, to simultaneouslypolish both front and back surfaces of the wafers, wherein the wafersare polished while controlling the turn table shape by adjusting theslurry supply amount.

In such a double-side polishing method for simultaneously polishing bothfront and back surfaces of wafers as described above, it is possible tocontrol polishing surface temperature by adjusting slurry supply amountduring polishing, thus allowing the turn table shape control withexcellent responsiveness. This ensures stability in polishing withoutdeteriorating wafer shape.

At this time, it is preferred that the slurry supply amount be adjustedin accordance with usage time of the polishing pads.

Thus, by adjusting slurry supply amount in accordance with usage time ofpolishing pads, it is possible to ensure good precision in the turntable shape control in accordance with changes in polishing ability andother factors of polishing pads over time. For instance, it suffices toadjust slurry supply amount such that supply amount is reduced withincreasing usage time of polishing pads. Thus, by adjusting slurrysupply amount, it is possible to conduct polishing stably withoutdeteriorating wafer shape even during repeated polishing of a pluralityof batches of wafers.

Further, a wafer double-side polishing method according to the presentinvention is a wafer double-side polishing method comprising holdingwafers in wafer holding holes formed on a carrier plate; and whilesupplying slurry, moving the carrier plate between upper and lower turntables to which polishing pads are attached, to simultaneously polishboth front and back surfaces of the wafers, wherein shape adjustmentmeans are disposed at load supporting point portions of the upper turntable, and wherein the wafers are polished while controlling the turntable shape by adjusting the shape adjustment means.

In such a double-side polishing method for simultaneously polishing bothfront and back surfaces of wafers as described above, it is possible, byproviding shape adjustment means at the load supporting point portionsof the upper turn table and conducting polishing while controlling theturn table shape through adjustment of the shape adjustment means, toforcibly deform the upper the turn table shape with the shape adjustmentmeans, allowing proper the turn table shape control in accordance withchanges in polishing ability and other factors of polishing pads overtime during wafer polishing. This ensures good precision and stabilityin wafer shape during polishing and allows precise wafer shape controland stable polishing without deteriorating wafer shape even duringrepeated polishing of a plurality of batches of wafers.

At this time, it is preferred that the motion of the carrier plate be acircular motion not accompanied by the rotation of the carrier plate.

Thus, by ensuring that the carrier plate motion is a circular motion notaccompanied by the rotation of the carrier plate, it is possible toconduct uniform polishing across both front and back surfaces of wafersheld by the carrier plate.

Further, according to the present invention, there is provided a waferdouble-side polishing method comprising holding wafers on a plurality ofcarrier plates each having thereon formed holding holes for holdingwafers; and while supplying slurry, rotating and revolving the pluralityof carrier plates using sun and internal gears between upper and lowerturn tables to which polishing pads are attached, to simultaneouslypolish both front and back surfaces of the wafers, wherein shapeadjustment means are disposed at load supporting point portions of theupper turn table, and wherein the wafers are polished while controllingthe turn table shape by adjusting the shape adjustment means.

In such a double-side polishing method for simultaneously polishing bothfront and back surfaces of wafers as described above, it is possible, byproviding shape adjustment means at the load supporting point portionsof the upper turn table and conducting polishing while controlling theturn table shape through adjustment of the shape adjustment means, toforcibly deform the upper the turn table shape with the shape adjustmentmeans, allowing proper the turn table shape control in accordance withchanges in polishing ability and other factors of polishing pads overtime during wafer polishing. This ensures good precision and stabilityin wafer shape during polishing and allows precise wafer shape controland stable polishing without deteriorating wafer shape even duringrepeated polishing of a plurality of batches of wafers.

At this time, it is preferred that the wafer be polished whilecontrolling the turn table shape by adjusting supply amount of theslurry supplied.

By providing shape adjustment means at the load supporting pointportions of the upper turn table as described above and thus furtheradjusting the slurry supply amount, it is possible to control the turntable shape with further high precision, reliably preventingdeterioration of wafer shape.

Further at this time, it is preferred that, the wafers be polished withcausing a PCD of upper turn table load supporting points that is adiameter of a circle joining load supporting points of the upper turntable and a PCD of wafer centers that is a diameter of a circle joiningcenters of the wafers held by the carrier plate to coincide with eachother, or causing the PCD of upper turn table load supporting points anda PCD of carrier plate centers that is a diameter of a circle joiningcenters of the plurality of carrier plates to coincide with each other.

In the double-side polishing method, by polishing with causing a PCD ofupper turn table load supporting points that is a diameter of a circlejoining the load supporting points of the upper turn table and a PCD ofwafer centers that is a diameter of a circle joining centers of thewafers held by the carrier plate to coincide with each other, or causingthe PCD of upper turn table load supporting points and a PCD of carrierplate centers that is a diameter of a circle joining centers of theplurality of carrier plates to coincide with each other, it is possibleto control the turn table shape with excellent responsiveness throughadjustment of the slurry supply amount or adjustment of the shapeadjustment means such as micrometers. This allows precise the turn tableshape control in response to change in wafer shape over time, ensuringgood precision in wafer shape control and stability in polishing evenduring repeated polishing of a plurality of batches of wafers.

As described above, according to the present invention, by causing,during wafer polishing, the PCD of upper turn table load supportingpoints and the average PCD of centers of wafers held by a carrier plateto coincide with each other or the PCD of upper turn table loadsupporting points and the PCD of centers of the plurality of carrierplates to coincide with each other, it is possible to provide turn tabledeformation with improved responsiveness, allowing precise wafer shapecontrol. Further, excellent responsiveness of turn table deformationallows stable wafer shape control with high precision by properlychanging polishing conditions during repeated polishing of a pluralityof batches of wafers.

Further, according to the present invention, by adjusting slurry supplyamount, or by providing shape adjustment means at load supporting pointportions of the upper turn table and adjusting the shape adjustmentmeans during wafer polishing, it is possible to control the turn tableshape with excellent responsiveness. This ensures good precision andstability in wafer shape during polishing, and it is possible to controlbatch-by-batch wafer shape with high precision and to perform stablypolishing without deteriorating wafer shape even during repeatedpolishing of a plurality of batches of wafers.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 illustrates a schematic sectional explanatory view showing anexample of double-side polishing apparatus associated with a firstembodiment of the present invention;

FIG. 2 illustrates a plan view of an upper turn table in the double-sidepolishing apparatus shown in FIG. 1;

FIG. 3 illustrates a plan view of a carrier plate in the double-sidepolishing apparatus shown in FIG. 1;

FIG. 4 illustrates a schematic sectional explanatory view showing anexample of another form of (four-way) double-side polishing apparatusassociated with the first embodiment of the present invention;

FIG. 5 illustrates a sectional explanatory view showing an example ofconventional double-side polishing apparatus;

FIG. 6 illustrates a graph showing wafer shape responsiveness to changesin polishing conditions in example 1 and comparative example 1;

FIG. 7 illustrates a graph evaluating wafer shape controllability duringrepeated polishing of a plurality of batches of wafers in example 2 andcomparative example 2;

FIG. 8 illustrates a graph evaluating wafer shape controllability duringrepeated polishing of a plurality of batches of wafers in example 3 andcomparative example 3;

FIG. 9 illustrates a schematic sectional explanatory view showing anexample of double-side polishing apparatus associated with a secondembodiment of the present invention;

FIG. 10 illustrates a schematic explanatory view showing deformation ofthe upper turn table through adjustment of shape adjustment means;

FIG. 11 illustrates a schematic sectional explanatory view showing anexample of another form of (four-way) double-side polishing apparatusassociated with the second embodiment of the present invention;

FIG. 12 illustrates a graph showing wafer shape responsiveness to changein slurry supply amount;

FIG. 13 illustrates a graph showing wafer shape responsiveness toadjustment of the shape adjustment means;

FIG. 14 illustrates a graph evaluating wafer shape controllabilityduring repeated polishing of a plurality of batches of wafers in example4; and

FIG. 15 illustrates a graph evaluating wafer shape controllabilityduring repeated polishing of a plurality of batches of wafers in example6.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be explained.However, the present invention is not limited thereto.

When wafers are repeatedly polished using a conventional double-sidepolishing apparatus as shown in FIG. 5, as the number of wafer batchesto be polished increases it has become difficult to control the turntable shape with high precision due to poor responsiveness of turn tabledeformation (e.g., linearly relative to changes in polishingconditions), making it impossible to control wafer shape stably and withhigh precision (first problem). Due to poor responsiveness of turn tabledeformation, it has been impossible to precisely control the turn tableinto a desired shape with turn table temperature control alone,hindering stability and high precision in wafer shape control (secondproblem).

To solve the first problem, therefore, the present inventors, as aresult of diligent study, perfected the present invention upondiscovering that, noting the relationship between supporting points ofthe upper turn table and the carrier plate position (or polished waferposition), it is possible to control the turn table shape with excellentresponsiveness in accordance with changes in polishing conditions, etc.by adjusting a positional relationship therebetween, and thereby it ispossible to repeatedly polish wafers while suppressing deterioration inwafer shape and maintaining good precision and stability in wafer shapeeven during repeated polishing of a plurality of batches of wafers.

Further, to solve the second problem, the present inventors, as a resultof diligent study, perfected the present invention upon devising that,as additional the turn table shape is controlled methods in addition toturn table temperature control, the turn table shape is controlledthrough adjustment of supply amount of slurry supplied during polishingand through adjustment of the shape adjustment means by providing theshape adjustment means at load supporting point portions of the upperturn table.

First, an example of wafer double-side polishing apparatus associatedwith a first embodiment of the present invention will be described withreference to accompanying drawings. FIG. 1 illustrates a schematicsectional explanatory view of a double-side polishing apparatusassociated with the first embodiment of the present invention. FIGS. 2and 3 illustrate plan views of an upper turn table and a carrier plate,respectively.

A double-side polishing apparatus 1 has a carrier plate 6 with waferholding holes, upper and lower turn tables 2 and 3 to which polishingpads 5 are attached and a slurry supply means 33 for supplying slurry,and can simultaneously polish both front and back surfaces of wafers 4by inserting the wafers 4 into and holding them in the wafer holdingholes on the carrier plate 6, sandwiching the wafers with the upper andlower turn tables 2 and 3 from above and below the wafers and rotatingthe upper and lower turn tables 2 and 3 on a rotation axis perpendicularto the wafers 4 while supplying slurry from the slurry supply means.

The upper turn table 2 is provided with a cylinder 7 for applyingrotation and polishing loads, a housing 8 for transmitting those loadsto the upper turn table 2 and fixing means 9 such as bolts for fixingthe housing 8 and the upper turn table 2, and further equipped withtemperature regulating means (not shown) therein for controlling theturn table temperature. Although the temperature regulating means arenot specifically limited, they are designed to supply cooling and hotwater into piping provided within the turn table.

On the other hand, the lower turn table 3 is provided with the cylinder7 for imparting rotation from a motor and a speed reducer (not shown) tothe lower turn table and thrust bearings 10 that support the load of theturn tables. The lower turn table is also equipped with temperatureregulating means not shown therein for controlling the turn tabletemperature as with the upper turn table.

The polishing pads 5 for mirror-polishing front and back surfaces of thewafers are attached to the under surface of the upper turn table 2 andthe top surface of the lower turn table 3 in the double-side polishingapparatus 1. Although types and materials of the polishing pads are notlimited, for example, hard polyurethane foam pads and soft non-wovencloth pads made by hardening polyurethane-resin-impregnated non-wovencloth, which are ordinary polishing pads, are among usable pads. As softnon-woven cloth, Suba600 manufactured by Rodel Inc. is employed, forexample. In addition, polishing pads of two or more layers made byfoaming polyurethane resin on top of a base cloth made of non-wovencloth can also be used.

The carrier plate 6 is, for example, a disk-shaped plate on which fivewafer holding holes 19 are formed as shown in FIG. 3. The wafers 4 areheld in the wafer holding holes 19 so as to be rotatable. Although thematerial and other properties of the carrier plate 6 are notspecifically limited, it is preferred that the carrier plate 6 made, forexample, of glass epoxy be used.

The perimeter portion of the carrier plate 6 is held by an annularportion 11(b) of a carrier holder 11, causing the carrier plate 6 tomake a circular motion in a plane (horizontal plane) parallel to thesurface of the carrier plate 6 without the carrier plate 6 itselfrotating. The perimeter of the annular portion 11(b) of the carrierholder 11 is provided with a plurality of bearing portions 11(a)projecting outward. An eccentric shaft 12(a) of an eccentric arm 12 inthe form of a small-diameter disk is attached by insertion to each ofthe bearing portions 11(a) of the carrier holder, with a rotary shaft12(b) installed vertically at a central portion of each of the undersurfaces of the eccentric arms 12. Further, a sprocket 13 is fastened tothe end of each of the rotary shafts 12(b), with a timing chain 14 beingstretched among each of the sprockets in a horizontal state in a serialmanner. The sprockets 13 and the timing chain 14 together constitutesynchronization means for rotating the plurality of eccentric arms 12synchronously.

Rotation is imparted to one of the sprockets 13 by operating a circularmotion motor (not shown) connected to one of the sprockets 13. As aresult of rotation of the timing chain 14 via the sprocket 13 to performcyclic motion of the timing chain, the plurality of eccentric arms 12rotate in synchronization on the rotary shafts 12(b) in a horizontalplane. This allows the carrier holder 11 coupled to each of theeccentric arms 12 and the carrier plate 6 held by the carrier holders 11to make a circular motion that is a circling taking place eccentricallyfrom the rotational axis of the upper and lower turn tables 2 and 3, ina horizontal plane parallel to the carrier plate, by the same distanceas that between the eccentric shaft 12(a) and the rotary shaft 12(b) inthe eccentric arm 12.

Thus, by causing the carrier plate to make a circular motion notaccompanied by the rotation of the carrier plate, all points on thecarrier plate 6 trace a small circular trajectory of the same size,allowing uniform polishing across both front and back surfaces of thewafers 4 held by the carrier plate 6.

In such the double-side polishing apparatus 1, it is possible, bycausing a PCD (Pitch Circle Diameter) of upper turn table loadsupporting points that is a diameter of a circle (pitch circle) joiningthe load supporting points of the upper turn table 2 and a PCD ofcenters of the wafer holding holes on the carrier plate that is adiameter of a circle (pitch circle) joining each center of the waferholding holes on the carrier plate 6 to coincide with each other, toprovide turn table deformation with improved responsiveness to changesin polishing conditions during wafer polishing, thus making thedouble-side polishing apparatus 1 capable of repeated wafer polishingwhile controlling polished wafer shape with high precision.

More specifically, the upper turn table 2 of the double-side polishingapparatus 1 is held to the housing 8 by the fixing means 9 such asbolts, with a given load applied during polishing. For this reason, loadsupporting points of the upper turn table 2 are located on the fixingmeans 9 that are joining portions between the upper turn table 2 and thehousing 8 as shown in FIG. 2. Consequently, the PCD of upper turn tableload supporting points can be expressed by a diameter 15 of a circle 16joining the centers of the fixing means 9 that are the load supportingpoints of the upper turn table. The PCD of centers of the wafer holdingholes on the carrier plate 6 can be, in the case of a double-sidepolishing apparatus with the single carrier plate 6 as described above,expressed by a diameter 18 of a circle 17 joining the centers of thewafer holding holes 19 (the centers roughly coincide with wafer centersof the wafers 4 held by the carrier plate 6) formed on the carrier plate6 as shown in FIG. 3.

It is possible to cause the PCD of upper turn table load supportingpoints and the PCD of centers of the wafer holding holes on the carrierplate to coincide with each other in design stage of double-sidepolishing apparatus by adjusting the upper turn table and the carrierplate. As for existing double-side polishing apparatuses, it is possibleand convenient to cause the PCD of upper turn table load supportingpoints and the PCD of centers of the wafer holding holes on the carrierplate to coincide with each other in carrier plate manufacture stage byadjusting the positions of wafer holding holes.

At this time, it is important to cause the PCD of upper turn table loadsupporting points and the PCD of centers of the wafer holding holes onthe carrier plate to coincide with each other, and it is preferred thatthese pitch circles be located at the same position during polishing.However, if the carrier plate 6 of the double-side polishing apparatus 1makes a circular motion that is a circling taking place eccentricallyfrom the rotational axis of the upper and lower turn tables as describedabove, although the diameter of the pitch circle formed by loadsupporting points of the upper turn table coincides with that formed bycenters of wafer holding holes of the carrier plate, the position of thepitch circle of centers of wafer holding holes on the carrier plate 6changes over time during polishing. Therefore, it is impossible toensure a constant coincidence between the pitch circle of turn tableload supporting points and the pitch circle of centers of the waferholding holes on the carrier plate. In this case, consequently, itsuffices to cause the pitch circle of upper turn table load supportingpoints and the circle joining the average position of small circulartrajectories of centers of the wafer holding holes on the carrier plate(wafer centers of wafers held by the carrier plate) to coincide witheach other, and coincidence of PCDs as referred to in the presentinvention includes coincidence of diameters and coincidence of suchpitch circle positions.

In the double-side polishing apparatus shown in FIG. 1, it is preferredthat a PCD of lower turn table load supporting points that is a diameterof a circle joining the load supporting points of the lower turn table 3coincide with the PCD of upper turn table load supporting points. Asdescribed above, in the double-side polishing apparatus 1 of the presentinvention, the lower turn table 3 is held by the thrust bearings 10,with a given load applied during polishing. Therefore, load supportingpoints of the lower turn table 3 are located on joining portions withthe thrust bearings 10. Consequently, the PCD of lower turn table loadsupporting points can be expressed by a diameter of a circle joiningfixing portions of the thrust bearings 10. Thus, by causing the PCD oflower turn table load supporting points to coincide with the PCD ofupper turn table load supporting points, it is possible to improvefurther responsiveness in the turn table shape control.

For coincidence the PCD of upper turn table load supporting points withthe PCD of centers of the wafer holding holes on the carrier plate(wafer centers of wafers held by the carrier plate) and coincidence thePCD of upper turn table load supporting points with the PCD of lowerturn table load supporting points, it suffices to cause these PCDs tocoincide with each other, including diameters and pitch circlepositions, within a tolerance of 5 mm or less. While perfectcoincidences are preferred between the PCD of upper turn table loadsupporting points and the PCD of centers of the wafer holding holes onthe carrier plate and between the PCD of upper turn table loadsupporting points and the PCD of lower turn table load supportingpoints, it is only natural that a certain amount of tolerance actuallyoccurs. In consideration of eccentricity during polishing, it ispossible to improve sufficiently responsiveness of turn tabledeformation to changes in polishing conditions by achieving acoincidence within a tolerance of 5 mm or less. That is, coincidence ofthe PCDs as referred to in the present invention may include cases inwhich such a certain amount of tolerance exists.

Next, a method for simultaneously polishing both front and back surfacesof wafers will be demonstrated using the double-side polishing apparatusshown in FIG. 1 in which the PCD of upper turn table load supportingpoints coincides with the PCD of centers of the wafer holding holes onthe carrier plate.

First, the wafers 4 are inserted into and held by the carrier plate 6 onwhich the wafer holding holes are formed. Then, the wafers 4 held by thecarrier plate 6 are sandwiched by the upper and lower turn tables 2 and3, to which the polishing pads 5 are attached, using an elevating device(not shown) for causing the upper and lower turn tables 2 and 3 toadvance or retreat along the rotational axis. Then, the upper turn table2 is rotated by an upper rotation motor (not shown) via the cylinder 7in a horizontal plane and the lower turn table 3 is rotated by a lowerrotation motor (not shown) via the cylinder 7 in a horizontal planewhile supplying slurry from the slurry supply means 33. At this time,the wafers 4 are held in the wafer holding holes on the carrier plate 6so as to be rotatable, allowing the wafers 4 to turn together (rotate)in the direction of rotation of the faster rotating turn table byadjusting the rotation speeds of the upper and lower turn tables 2 and3. At the same time the upper and lower turn tables 2 and 3 are rotated,the carrier plate 6 is caused to make a circular motion not accompaniedby its rotation by the carrier holders 11 to which the eccentric arms 12are attached by insertion. Thus, the PCD of upper turn table loadsupporting points coincides with the PCD of centers of the wafer holdingholes on the carrier plate and further with the PCD of lower turn tableload supporting points, making it possible to polish uniformly bothfront and back surfaces of the wafers 4 simultaneously.

At this time, neither rotation speeds of the upper and lower turn tables2 and 3 nor their rotation directions nor pressing forces applied to thewafers 4 by the upper and lower turn tables 2 and 3 are limited. It ispreferred that pressing on front and back surfaces of the silicon wafersby the upper and lower turn tables 2 and 3 be applied by a pressureapplication method via a fluid, etc. Pressure is applied primarily by ahousing portion arranged on the upper turn table. Normally, pressingforces applied to the wafers by the upper and lower turn tables are 100to 300 g/cm2. At this time, polishing amount and polishing speed infront and back surfaces of the wafers are not particularly limited.

The slurry supply means 33 can be, for example, constituted by forming aplurality of slurry supply holes on the upper turn table. It ispreferred that the plurality of slurry supply holes be constituted suchthat slurry is constantly supplied to the wafer surfaces even in theevent of wafer swinging and that the slurry supply holes be arranged inan area in the form of an annular ring of a given width in which thewafers always exist. In this case, type of slurry used is not limited.For instance, when silicon wafers are polished, alkali solution with pH9to 11 containing colloidal silica can be used. Although slurry supplyamount is not limited since the amount varies depending on the carrierplate size, the amount is normally 2.0 to 6.0 liters/min.

Thus, by polishing the wafers with causing the PCD of upper turn tableload supporting points that is the diameter of the circle joining theload supporting points of the upper turn table and the PCD of wafercenters that is the diameter of the circle joining centers of the wafersheld by the carrier plate to coincide with each other, it is possible toimprove responsiveness of the turn table shape control to changes inpolishing conditions. Therefore, by improving responsiveness of turntable deformation as described above during simultaneous polishing ofboth front and back surfaces of the wafers and by conducting waferpolishing while controlling polishing conditions such as the upperand/or lower turn table temperature, it is possible to conduct polishingwhile easily controlling wafer shape through the turn table shapedeformation so as to compensate for variations in polished wafer shapeassociated with progress of polishing. This allows suppression of changein wafer shape over time and ensures good precision and stability inwafer shape control without deteriorating wafer shape during polishingof a plurality of batches of wafers.

Note that although, in the aforementioned double-side polishingapparatus, it was explained about a case in which a plurality of wafersare held by the carrier plate and wafer polishing is performed, thepresent invention is not limited thereto. For instance, the presentinvention is also applicable to a case in which wafers are held one byone on the carrier plate (single wafer processing) and wafer polishingis performed. In this case, a similar effect can be achieved by causingthe PCD of upper turn table load supporting points and the diameter ofthe wafer held by the carrier plate to coincide with each other, and thepresent invention includes such a case.

Next, another form of double-side polishing apparatus associated withthe first embodiment of the present invention will be described. FIG. 4illustrates a schematic sectional explanatory view of a four-waydouble-side polishing apparatus in accordance with the presentinvention.

A four-way double-side polishing apparatus 21 has a plurality of carrierplates 26 with wafer holding holes, sun and internal gears 31 and 32 forrotating and revolving the carrier plates, upper and lower turn tables22 and 23 to which polishing pads 25 are attached and a slurry supplymeans 34, and can simultaneously polish both front and back surfaces ofwafers 24 by inserting the wafers 24 into and holding them in the waferholding holes on the plurality of carrier plates 26, sandwiching theplurality of carrier plates 26 with the upper and lower turn tables 22and 23, to which the polishing pads 25 are attached, from above andbelow the carrier plates, rotating and revolving the carrier plates withthe sun and internal gears 31 and 32 while supplying slurry from theslurry supply means and rotating the upper and lower turn tables 22 and23 on a rotational axis perpendicular to the wafers 24.

At this time, the upper turn table 22 is provided with a cylinder 27 forapplying rotation and polishing loads, a housing 28 for transmittingthose loads to the upper turn table and fixing means 29 such as boltsfor fixing the housing and the upper turn table, and further equippedwith temperature regulating means (not shown) therein for controllingthe turn table temperature. On the other hand, the lower turn table 23is provided with the cylinder 27 for imparting rotation from a motor anda speed reducer (not shown) to the lower turn table and thrust bearings30 that support the load of the turn tables. The lower turn table 23 isalso equipped with temperature regulating means (not shown) therein forcontrolling the turn table temperature.

For use as the polishing pads 25 attached to the under surface of theupper turn table 22 and the top surface of the lower turn table 23 inthe double-side polishing apparatus 21, hard polyurethane foam pads andsoft non-woven cloth pads made by hardeningpolyurethane-resin-impregnated non-woven cloth, which are ordinarypolishing pads, are among usable pads as mentioned earlier.

Thus, by causing, in the double-side polishing apparatus 21, a PCD ofupper turn table load supporting points that is a diameter of a circlejoining the load supporting points of the upper turn table 22 and a PCDof carrier plate centers that is a diameter of a circle joining centersof the plurality of carrier plates 26 to coincide with each other, it ispossible to improve responsiveness of turn table deformation to changesin polishing conditions during wafer polishing, thus making thedouble-side polishing apparatus capable of repeated wafer polishingwhile controlling wafer shape with high precision.

More specifically, the upper turn table 22 of the double-side polishingapparatus 21 is held to the housing 28 by the fixing means 29 such asbolts as described above. For this reason, load supporting points of theupper turn table 22 are located on the fixing means 29 that are joiningportions between the upper turn table 22 and the housing 28.Consequently, the PCD of upper turn table load supporting points can beexpressed by the diameter of the circle joining the centers of thefixing means 29 that are load supporting points of the upper turn table.Since a plurality of wafer holding holes are formed on the carrierplates in such a double-side polishing apparatus, it is difficult tocause the average PCD of centers of wafer holding holes of the carrierplates (centers of wafers held by the carrier plates) to coincide withthe PCD of upper turn table load supporting points. In the case of thedouble-side polishing apparatus 21, for this reason, the PCD of carrierplate centers that is the diameter of the circle joining centers of theplurality of carrier plates 26 is caused to coincide with the PCD ofupper turn table load supporting points.

Further, it is preferred that a PCD of lower turn table load supportingpoints that is a diameter of a circle joining the load supporting pointsof the lower turn table 23 coincides with the PCD of the upper turntable load supporting points. Since the lower turn table is held by thethrust bearings 30 in the double-side polishing apparatus 21 asdescribed above, load supporting points of the lower turn table 23 arelocated on joining portions with the thrust bearings 30. Consequently,the PCD of lower turn table load supporting points can be expressed by adiameter of a circle joining fixing portions of the thrust bearings 30.Thus, by causing the PCD of lower turn table load supporting points tocoincide with the PCD of the upper turn table load supporting points, itis possible to further improve responsiveness of the turn table shapecontrol.

At this time, while perfect coincidences are preferred between the PCDof upper turn table load supporting points and the PCD of carrier platecenters and between the PCD of upper turn table load supporting pointsand the PCD of lower turn table load supporting points, it suffices toachieve a coincidence within a tolerance of 5 mm or less as mentionedearlier, thus improving responsiveness of turn table deformation tochanges in polishing conditions. The present invention includes such acase.

Next, a method for simultaneously polishing both front and back surfacesof wafers will be demonstrated using a four-way double-side polishingapparatus in which the PCD of upper turn table load supporting pointscoincides with the PCD of carrier plate centers.

First, the wafers 24 are inserted into and held by the plurality ofcarrier plates 26 on which wafer holding holes are formed. Then, thewafers 24 held by the carrier plate 26 are sandwiched by the upper andlower turn tables 22 and 23, to which the polishing pads 25 areattached, using an elevating device (not shown) for causing the upperand lower turn tables 22 and 23 to advance or retreat along therotational axis. Then, the upper turn table 22 is rotated by an upperrotation motor (not shown) via the cylinder 27 in a horizontal plane andthe lower turn table 23 is rotated by a lower rotation motor (not shown)via the cylinder 27 in a horizontal plane while supplying slurry fromthe slurry supply means 34. By rotating and revolving the plurality ofcarrier plates 26 with the sun and internal gears 31 and 32 concurrentlywith the rotation of the upper and lower turn tables 22 and 23, it ispossible to uniformly polish both front and back surfaces of the wafers.

At this time, neither rotation speeds nor rotation directions of theupper and lower turn tables nor pressing forces applied to the wafers bythe upper and lower turn tables, etc. are limited, and polishing can becarried out in conventional polishing conditions.

Thus, by using a four-way double-side polishing apparatus and polishingthe wafers with causing the PCD of upper turn table load supportingpoints that is the diameter of the circle joining the load supportingpoints of the upper turn table and the PCD of carrier plate centers thatis the diameter of the circle joining centers of the plurality ofcarrier plates to coincide with each other, it is possible to improveresponsiveness of turn table deformation to changes in polishingconditions. Therefore, by improving responsiveness of turn tabledeformation as described above for wafer polishing and by conductingwafer polishing while controlling polishing conditions such as the upperand/or lower turn table temperature, it is possible to conduct polishingwhile easily controlling wafer shape through the turn table shapedeformation so as to compensate for variations in polished wafer shapeassociated with progress of polishing. This allows suppression of changein wafer shape over time and ensures good precision and stability inwafer shape control without deteriorating wafer shape even duringpolishing of a plurality of batches of wafers.

Next, an example of wafer double-side polishing apparatus associatedwith the second embodiment of the present invention will be describedwith reference to accompanying drawings. FIG. 9 illustrates a schematicsectional explanatory view of a double-side polishing apparatusassociated with the second embodiment of the present invention.

A double-side polishing apparatus 101 has a carrier plate 106 with waferholding holes, upper and lower turn tables 102 and 103 to whichpolishing pads 105 are attached and slurry supply means 116 forsupplying slurry and can simultaneously polish both front and backsurfaces of wafers 104 by inserting the wafers 104 into and holding themin the wafer holding holes on the carrier plate 106, sandwiching thewafers with the upper and lower turn tables 102 and 103 from above andbelow the wafers and rotating the upper and lower turn tables 102 and103 on a rotational axis perpendicular to the wafers 104 while supplyingslurry from the slurry supply means 116.

The upper turn table 102 is provided with a cylinder 107 for applyingrotation and polishing loads, a housing 108 for transmitting those loadsto the upper turn table 102 and fixing means 109 such as bolts forfixing the housing 108 and the upper turn table 102, and furtherequipped with temperature regulating means (not shown) therein forcontrolling the turn table temperature. Although the temperatureregulating means are not specifically limited, they are designed tosupply cooling and hot water into piping provided within the turn table.

The upper turn table 102 is held to the housing 108 by the fixing means109 such as bolts, and a given load is applied to the upper turn table102 during wafer polishing. For this reason, load supporting points ofthe upper turn table 102 are located on the fixing means 109 that arejoining portions between the upper turn table 102 and the housing 108.

In the double-side polishing apparatus 101 of the present invention, itis possible to mechanically press and forcibly deform the upper turntable 102 by providing shape adjustment means 115 at load supportingpoint portions near the fixing means 109 that are load supporting pointsof the upper turn table 102, for example, at two points of perimeter andcenter sides of the fixing means 109 as shown in FIG. 9 and by adjustingthe provided shape adjustment means 115. Thus, the double-side polishingapparatus of the present invention can forcibly and precisely controlthe shape of the upper turn table 102 during wafer polishing byadjusting the shape adjustment means 115 in accordance with changes inpolishing ability and other factors of the polishing pads 105 over time,thus ensuring high precision and stability in wafer polishing.

At this time, although the shape adjustment means 115 are notspecifically limited, it is preferred that the shape adjustment means115 be, for example, micrometers. Thus, if the shape adjustment meansare micrometers, it is possible to mechanically press the upper turntable by a desired magnitude and to forcibly deform the upper turn tablethrough accurate adjustment of the micrometers, allowing precisedeformation of the turn table into a desired shape.

On the other hand, the lower turn table 103 is provided with thecylinder 107 for imparting rotation from a motor and a speed reducer(not shown) to the lower turn table and thrust bearings 110 that supportthe load of the turn tables. The lower turn table 103 is also equippedwith temperature regulating means therein that are not shown forcontrolling the turn table temperature as with the upper turn table.

It is preferred that materials of the upper and lower turn tables 102and 103 be stainless steel (SUS). Thus, if the turn tables are made ofstainless steel (SUS), it is possible to properly deform the turntables, allowing easy deformation of the turn tables with the shapeadjustment means, etc. Although types and materials of the polishingpads 105, attached to the under surface of the upper turn table 102 andthe top surface of the lower turn table 103 for mirror-polishing frontand back surfaces of the wafers, are not limited, hard polyurethane foampads and soft non-woven cloth pads made by hardeningpolyurethane-resin-impregnated non-woven cloth, which are ordinarypolishing pads, are among usable pads, for example. As soft non-wovencloth, Suba600 manufactured by Rodel Inc. is employed, for example. Inaddition, polishing pads of two or more layers made by foamingpolyurethane resin on top of a base cloth made of non-woven cloth canalso be used.

The slurry supply means 116 are constituted by providing slurry supplyholes on the upper turn table via a rotary joint (not shown) and canchange slurry supply amount, for example, by a solenoid valve that isnot shown and the like. The plurality of slurry supply means can beformed, and it is preferred that the slurry supply means be arranged inan area in the form of an annular ring of a given width in which thewafers always exist such that slurry is constantly supplied to the wafersurfaces even if the carrier plate performs a swinging motion.

The carrier plate 106 has, for example, five wafer holding holes formedon a disk-shaped plate and can hold the wafers 104 so as to be rotatablein the wafer holding holes. Although the material and other propertiesof the carrier plate 106 are not specifically limited, it is preferredthat the carrier plate 106 made, for example, of glass epoxy be used.

The perimeter portion of the carrier plate 106 is held by an annularportion 111(b) of a carrier holder 111, causing the carrier plate 106 tomake a circular motion in a plane (horizontal plane) parallel to thesurface of the carrier plate without the carrier plate itself rotating.The perimeter of the annular portion 111(b) of the carrier holder 111 isprovided with a plurality of bearing portions 111(a) projecting outward.An eccentric shaft 112(a) of an eccentric arm 112 in the form of asmall-diameter disk is attached by insertion to each of the bearingportions 111(a) of the carrier holder, with a rotary shaft 112(b)installed vertically at a central portion of each of the under surfacesof the eccentric arm 112. Further, a sprocket 113 is fastened to the endof each of the rotary shafts 112(b), with a timing chain 114 beingstretched among each of the sprockets 113 in a horizontal state in aserial manner. The sprockets 113 and the timing chain 114 togetherconstitute synchronization means for rotating the plurality of eccentricarms 112 synchronously.

Rotation is imparted to one of the sprockets 113 by operating a circularmotion motor (not shown) connected to one of the sprockets 113. As aresult of rotation of the timing chain 114 via the sprocket 113 andcyclic motion of the timing chain, the plurality of eccentric arms 112rotate in synchronization on the rotary shafts 112(b) in a horizontalplane. This allows the carrier holder 111 coupled to each of theeccentric arms 112 and the carrier plate 106 held by the carrier holders111 to make a circular motion that is a circling taking placeeccentrically from the rotational axis of the upper and lower turntables 102 and 103, in a horizontal plane parallel to the carrier plate,by the same distance as that between the eccentric shaft 112(a) and therotary shaft 112(b) in the eccentric arm 112.

Thus, by causing the carrier plate 106 to make a circular motion notaccompanied by the rotation of the carrier plate, all points on thecarrier plate 106 trace a small circular trajectory of the same size,allowing uniform polishing across both front and back surfaces of thewafers 104 held by the carrier plate 106.

In such the double-side polishing apparatus 101, it is preferred that aPCD (Pitch Circle Diameter) of upper turn table load supporting pointsthat is a diameter of a circle joining the load supporting points of theupper turn table 102 coincide with a PCD of centers of the wafer holdingholes on the carrier plate that is a diameter of a circle joining theeach center of wafer holding holes on the carrier plate 106.

More specifically, load supporting points of the upper turn table 102 inthe double-side polishing apparatus 101 are located on the fixing means109 that are joining portions between the upper turn table 102 and thehousing 108 as described above. Consequently, the PCD of upper turntable load supporting points can be expressed by the diameter of thecircle (pitch circle) joining the centers of the fixing means 109 thatare the load supporting points of the upper turn table. The PCD ofcenters of wafer holding holes on the carrier plate 106 can be, in thecase of a double-side polishing apparatus with the single carrier plate6 as described above, expressed by the diameter of the pitch circlejoining the centers of the wafer holding holes (the centers roughlycoincide with wafer centers of the wafers 104 held by the carrier plate106) formed on the carrier plate 106.

It is possible, by causing the PCD of upper turn table load supportingpoints and the PCD of centers of the wafer holding holes on the carrierplate to coincide with each other, to improve responsiveness of turntable deformation (particularly, linearity) to adjustments of polishingslurry supply amount and the shape adjustment means during waferpolishing, and thereby making the double-side polishing apparatuscapable of stable wafer polishing while controlling polished wafer shapewith high precision.

It is possible to cause the PCD of upper turn table load supportingpoints and the PCD of centers of the wafer holding holes on the carrierplate to coincide with each other in design stage of double-sidepolishing apparatus by adjusting the upper turn table and the carrierplate. As for existing double-side polishing apparatuses, it is possibleand convenient to cause the PCD of upper turn table load supportingpoints and the PCD of centers of the wafer holding holes on the carrierplate to coincide with each other in carrier plate manufacture stage byadjusting the positions of wafer holding holes.

At this time, it is important to cause the PCD of upper turn table loadsupporting points and the PCD of centers of the wafer holding holes onthe carrier plate to coincide with each other, and it is preferred thatthese pitch circles be located at the same position during polishing.However, if the carrier plate 106 of the double-side polishing apparatus101 makes a circular motion that is a circling taking placeeccentrically from the rotational axis of the upper and lower turntables as described above, although the diameter of the pitch circleformed by load supporting points of the upper turn table coincides withthat formed by centers of wafer holding holes of the carrier plate, theposition of the pitch circle of centers of wafer holding holes on thecarrier plate 106 changes over time during polishing. Therefore, it isimpossible to ensure a constant coincidence between the pitch circle ofturn table load supporting points and the pitch circle of centers of thewafer holding holes on the carrier plate. In this case, consequently, itsuffices to cause the pitch circle of upper turn table load supportingpoints and the circle joining the average position of small circulartrajectories of centers of wafer holding holes on the carrier plate(wafer centers of wafers held by the carrier plate) to coincide witheach other, and coincidence of PCDs as referred to in the presentinvention includes coincidence of diameters and coincidence of suchpitch circle positions.

For coincidence of the PCD of upper turn table load supporting pointswith the PCD of centers of the wafer holding holes on the carrier plate(wafer centers of wafers held by the carrier plate) described above, itsuffices to cause the PCDs to coincide with each other, includingdiameters and pitch circle positions, within a tolerance of 5 mm orless. While a perfect coincidence is preferred between the PCD of upperturn table load supporting points and the PCD of centers of the waferholding holes on the carrier plate, it is only natural that a certainamount of tolerance actually occurs. In consideration of eccentricityduring polishing, it is possible to improve sufficiently responsivenessof turn table deformation to changes in polishing conditions byachieving a coincidence within a tolerance of 5 mm or less. That is,coincidence of the PCDs as referred to in the present invention mayinclude cases in which such a certain amount of tolerance exists.

Next, a method for simultaneously polishing both front and back surfacesof wafers will be demonstrated using the double-side polishing apparatus101 shown in FIG. 9.

First, the wafers 104 are inserted into and held by the carrier plate106 on which the wafer holding holes are formed. Then, the wafers 104held by the carrier plate 106 are sandwiched by the upper and lower turntables 102 and 103, to which the polishing pads 105 are attached, usingan elevating device (not shown) for causing the upper and lower turntables 102 and 103 to advance or retreat along the rotational axis.Then, the upper turn table 102 is rotated by an upper rotation motor(not shown) via the cylinder 107 in a horizontal plane and the lowerturn table 103 is rotated by a lower rotation motor (not shown) via thecylinder 107 in a horizontal plane while supplying slurry from theslurry supply means 116. At this time, the wafers 104 are held in thewafer holding holes on the carrier plate 106 so as to be rotatable,allowing the wafers 104 to turn together (rotate) in the direction ofrotation of the faster rotating turn table by adjusting the rotationspeeds of the upper and lower turn tables 102 and 103. At the same timethe upper and lower turn tables 102 and 103 are rotated, the carrierplate 106 is caused to make a circular motion not accompanied by itsrotation by the carrier holders 111 to which the eccentric arms 112 areattached by insertion. Thereby, it is possible to polish uniformly bothfront and back surfaces of the wafers 104 simultaneously.

At this time, neither rotation speeds of the upper and lower turn tables102 and 103 nor their rotation directions nor pressing forces applied tothe wafers 104 by the upper and lower turn tables 102 and 103 arelimited. It is preferred that pressing on front and back surfaces of thesilicon wafers by the upper and lower turn tables be applied by apressure application method via a fluid, etc. Pressure is appliedprimarily by a housing portion arranged on the upper turn table.Normally, pressing forces applied to the wafers by the upper and lowerturn tables are 100 to 300 g/cm². At this time, polishing amount andpolishing speed in front and back surfaces of the wafers are notlimited.

Thus, by adjusting amount of slurry supplied from the slurry supplymeans 116 during simultaneous polishing of both front and back surfacesof the wafers, it is possible to control polishing surface temperature,thus allowing polishing wafers while controlling the turn table shapewith excellent responsiveness.

Although slurry supply amount supplied from the slurry supply means isnot limited since the amount varies depending on conditions of thecarrier plate size and the like, the amount is normally 2.0 to 6.0liters/min. At this time, it is possible to control polishing surfacetemperature during polishing and control the turn table shape withexcellent responsiveness by adjusting slurry supply amount. This ensuresstable polishing without deteriorating wafer shape. At this time,although type of slurry used is not limited, alkali solution with pH 9to 11 containing colloidal silica can be used, for instance, forpolishing of silicon wafers.

At this time, it is preferred that slurry supply amount be adjusted inaccordance with usage time of the polishing pads. This ensures goodprecision in the turn table shape control in accordance with changes inpolishing ability and other factors of polishing pads over time. Forinstance, it suffices to adjust slurry supply amount such that supplyamount is reduced over time with increasing usage time of the polishingpads to maintain wafer shape within a range up to a control targetvalue, and the rate is set as appropriate according to the polishingapparatus and the polishing conditions used. For example, by adjustingslurry supply amount such that supply amount is reduced by about 0.2liters/min each time after polishing of five batches of wafers, it ispossible to deform the turn table shape so as to compensate forvariations in wafer shape associated with progress of polishing, thusallowing polishing while easily controlling wafer shape. This allowssuppression of change in wafer shape over time and ensures goodprecision in wafer shape control and stability in polishing withoutdeteriorating wafer shape during polishing of a plurality of batches ofwafers.

By providing shape adjustment means at the load supporting pointportions of the upper turn table and conducting polishing whilecontrolling the turn table shape through adjustment of the shapeadjustment means during simultaneous polishing of both front and backsurfaces of the wafers as described above, it is possible to forciblydeform the upper the turn table shape with the shape adjustment means,allowing proper the turn table shape control in accordance with changein wafer shape over time.

For instance, as shown in FIG. 10( a), the micrometers exemplified aboveare provided as the shape adjustment means 115 at two points ofperimeter and center sides of the fixing means 109 that are loadsupporting points of the upper turn table 102, and the two micrometersprovided at load supporting point portions are adjusted in order thatthe micrometer provided on the perimeter side of the fixing means 109may be loosened upward and the other micrometer provided on the centerside may be pressed downward, so that it is possible to control theshape of the upper turn table 102 into a downwardly convex shape asshown in FIG. 10( b). Conversely, by adjusting the micrometers in orderthat the micrometer provided on the perimeter side of the fixing means109 may be pressed downward and the other micrometer provided on thecenter side may be loosened upward, it is possible to control the shapeof the upper turn table 102 into an upwardly convex shape as shown inFIG. 10( c).

At this time, micrometer adjustment amount is determined by clarifyingin advance the relationship between polishing conditions such aspolishing temperature and change in wafer shape. By properly adjustingthe micrometers based on the relationship between polishing conditionsand wafer shape, it is possible to deform the turn table shape so as tocompensate for variations in wafer shape associated with progress ofpolishing, thus allowing polishing while easily controlling wafer shape.This allows suppression of change in wafer shape over time and ensuresgood precision in wafer shape control and stability in polishing withoutdeteriorating wafer shape during polishing of a plurality of batches ofwafers.

Further at this time, it is preferred that, the wafers be polished withcausing the PCD of upper turn table load supporting points that is thediameter of the circle joining the load supporting points of the upperturn table and the PCD of wafer centers that is the diameter of thecircle joining centers of the wafers held by the carrier plate tocoincide with each other. Thus, by causing the PCD of upper turn tableload supporting points and the PCD of wafer centers to coincide witheach other, it is possible to improve further responsiveness of turntable shape control by the adjustment of slurry supply amount and theadjustment of the shape adjustment means, thus ensuring high precisionin the turn table shape control. Therefore, it is possible to controlthe turn table shape precisely so as to compensate for changes in wafershape over time associated with progress of polishing, thus enablingpolishing while easily controlling wafer shape. Consequently, it ispossible to maintain wafer shape precisely and polish the wafers stablyeven during repeated polishing of a plurality of batches of wafers.

To evaluate responsiveness of turn table deformation to change in(adjustment of) slurry supply amount and responsiveness of turn tabledeformation to adjustment of the shape adjustment means, the results ofexperiments in relation to wafer shape responsiveness (linearity inparticular) will be shown below that were conducted by polishing wafersunder variation of slurry supply amount or adjustment of the shapeadjustment means.

The double-side polishing apparatus shown in FIG. 9 was used as waferdouble-side polishing apparatus. In the double-side polishing apparatus,the PCD of upper turn table load supporting points and the PCD ofcenters of the wafer holding holes on the carrier plate were coincidentat 600 mm. The average position of pitch circles formed by centers ofwafer holding holes on the carrier plate and the position of the pitchcircle formed by load supporting points of the upper turn table werecaused to coincide with each other when the carrier plate performscircular motion not accompanied by its rotation. Micrometers wereprovided as the shape adjustment means 115 at two points of perimeterand center sides of the fixing means 109 that are load supporting pointsof the upper turn table 102 to forcibly deform the turn table shape.

Using the double-side polishing apparatus, five silicon wafers havingdiameter of 300 mm (one batch) were first inserted into respective waferholding holes of the carrier plate (carrier plate having five waferholding holes) so as to be rotatable. Each wafer was pressed at 200g/cm² by the upper and lower turn tables to which soft non-woven cloths(polishing pads) were attached.

Then, both front and back surfaces of the wafers were polished, with theupper and lower polishing pads pressed against front and back surfacesof the wafers, by rotating the upper and lower turn tables whilesupplying slurry from the upper turn table side and by causing thecarrier plate to make a circular motion (circular motion of about 10 cmin diameter) not accompanied by the rotation of the carrier platethrough cyclic motion of the timing chain using a circular motion motor.Note that the slurry used was that in which polishing abrasive grainconsisting of colloidal silica of 0.05 μm in grain size was dispersed inalkali solution with pH 10.5.

(Responsiveness of Turn Table Deformation to Change in (Adjustment of)Slurry Supply Amount)

In order to evaluate responsiveness of turn table deformation to changein (adjustment of) slurry supply amount, slurry supply amount was variedin five steps at equal intervals for examination of responsiveness ofwafer shape to change in slurry supply amount. Slurry supply amount inexperimental condition 1 was actually set to 3.0 liters/min, with theamount increased each time by 0.2 liters/min in each of experimentalconditions 2 to 5, to examine the change in wafer shape (the change inthe turn table shape) according to change in slurry supply amount. Atthis time, other conditions were kept unchanged to the extent possible.For polishing pads in particular, the pads with similar usage times wereused for the experiment.

In this case, while responsiveness of turn table deformation may beevaluated by direct observation of change in the turn table shape, theshape of polished wafer is actually important. In the presentexperiment, for this reason, responsiveness of wafer shape to change inslurry supply amount was evaluated by measuring unevenness of wafersafter polishing and confirming thicknesses at the center and perimeterportions as parameters representing wafer shape. In this measurement,variations were relatively evaluated by using the shape of experimentalcondition 3 as reference and treating the shapes more convex as positiveand those more concave as negative.

(Responsiveness of the Turn Table Shape to Adjustment of the ShapeAdjustment Means)

In order to evaluate responsiveness of the turn table shape toadjustment of the shape adjustment means, wafers were polished underfive varying conditions of the turn table shape by adjusting upwardly ordownwardly the micrometer on the perimeter side and that on the centerside provided near the housing in the upper turn table.

Using the state in experimental condition 3 (the micrometer at theperimeter side set at the same height as that on the center side) asreference, the state in which the micrometer on the perimeter side wasupward loosened was treated as experimental condition 2, and the statein which the micrometer on the center side was furthermore presseddownward was treated as experimental condition 1. Conversely, usingexperimental condition 3 as reference, the state in which the micrometeron the center side was upward loosened was treated as experimentalcondition 4, and the state in which the micrometer on the perimeter sidewas furthermore pressed downward was treated as experimental condition5. Namely, the upper the turn table shape was controlled so as to bedownwardly convex in experimental conditions 1 and 2 as shown in FIG.10( b) and upwardly convex in experimental conditions 4 and 5 as shownin FIG. 10( c) to confirm change in wafer shape to adjustment of theshape adjustment means.

At this time, other conditions were kept unchanged to the extentpossible. For polishing pads in particular, the pads with similar usagetimes were used for the experiment. Responsiveness of wafer shape toadjustment of the shape adjustment means was evaluated by measuring, asa parameter representing wafer shape, unevenness of wafers afterpolishing as was done in the previous evaluation.

FIG. 12 shows measurement results of wafer shape responsiveness tochange in slurry supply amount and FIG. 13 shows measurement results ofwafer shape responsiveness to adjustment of the shape adjustment means.The measurement results are plotting of average values of five wafers(one batch) in each experimental condition. When slurry supply amount ischanged, it is apparent as shown in FIG. 12 that the linearity is good(correlation coefficient: 0.998) and that the responsiveness of wafershape (that is, responsiveness of turn table deformation) to change inslurry supply amount is good. When the shape adjustment means areadjusted, it is also apparent as shown in FIG. 13 that the linearity isgood (correlation coefficient: 0.995) and that the responsiveness ofwafer shape (that is, responsiveness of turn table deformation) tochange in the shape adjustment means is good.

From the experimental results, it is clear that the responsiveness ofturn table deformation to adjustment of slurry supply amount or of theshape adjustment means is very good. Therefore, it is possible toperform polishing stably with high precision without deteriorating wafershape, for example, by adjusting slurry supply amount or the shapeadjustment means in consideration of wafer shape responsiveness(linearity) shown in FIGS. 12 and 13 so as to compensate for variationsin wafer shape arising as a result of continuous and repeated polishingwith the same polishing pads.

While adjustment of slurry supply amount and the shape adjustment meanscontributes to precision in the turn table shape control even ifconducted separately, adjustment of both, furthermore in conjunctionwith adjustment of the turn table temperature with the temperatureregulating means in the turn tables, permit more precise and easycontrol in the turn table shape. This ensures higher precision in wafershape control and more stability in polishing. This also allowsmaintaining of batch-by-batch wafer shape with extremely high precisionand ensures stable polishing even during repeated polishing of aplurality of batches of wafers.

The turn table shape control through adjustment of slurry supply amountand adjustment of the shape adjustment means may be conducted everypolishing batch or in the middle of polishing. Normally, it is possibleto sufficiently control wafer shape by making adjustment every polishingbatch. It is possible that, for example, wafer shape is examined afterpolishing of several batches of wafers, and the turn table shape iscontrolled through adjustment of slurry supply amount and/or adjustmentof the shape adjustment means in accordance with change in wafer shapeover time, followed by performing polishing of a next batch.

Next, another form of double-side polishing apparatus associated withthe second embodiment of the present invention will be described. FIG.11 illustrates a schematic sectional explanatory view of a four-waydouble-side polishing apparatus in accordance with the presentinvention.

A four-way double-side polishing apparatus 121 has a plurality ofcarrier plates 126 with wafer holding holes, sun and internal gears 131and 132 for rotating and revolving the carrier plates, upper and lowerturn tables 122 and 123 to which polishing pads 125 are attached and aslurry supply means 134, and can simultaneously polish both front andback surfaces of wafers 124 by inserting the wafers 124 into and holdingthem in the wafer holding holes on the plurality of carrier plates 126,sandwiching the carrier plates 126 with the upper and lower turn tables122 and 123, to which the polishing pads 125 are attached, from aboveand below the carrier plates, rotating and revolving the carrier plates126 with the sun and internal gears 131 and 132 while supplying slurryfrom the slurry supply means and rotating the upper and lower turntables 122 and 123 on a rotational axis perpendicular to the wafers 124.

At this time, the upper turn table 122 is provided with a cylinder 127for applying rotation and polishing loads, a housing 128 fortransmitting those loads to the upper turn table and fixing means 129such as bolts for fixing the housing 128 and the upper turn table 122and further equipped with temperature regulating means (not shown)therein for controlling the turn table temperature.

Load supporting points of the upper turn table 122 are located on thefixing means 129 that are joining portions between the upper turn table122 and the housing 128. In the double-side polishing apparatus 121 ofthe present invention, it is possible to mechanically press and forciblydeform the upper turn table 122 by providing shape adjustment means 133at load supporting point portions near the fixing means 129 that areload supporting points of the upper turn table 122, for example, at twopoints of perimeter and center sides of the fixing means 129 as shown inFIG. 11 and by adjusting the provided shape adjustment means 133. Thus,the double-side polishing apparatus of the present invention canforcibly and precisely control the shape of the upper turn table 122during wafer polishing by adjusting the shape adjustment means 133 inaccordance with changes in polishing ability and other factors of thepolishing pads 125 over time, thus ensuring high precision and stabilityin wafer polishing.

At this time, although the shape adjustment means 133 are notspecifically limited, it is preferred that the shape adjustment means133 be, for example, micrometers. Thus, if the shape adjustment meansare micrometers, it is possible to mechanically press the upper turntable by a desired magnitude and to forcibly deform the upper turn tablethrough accurate adjustment of the micrometers, allowing precisedeformation of the turn table into a desired shape.

On the other hand, the lower turn table 123 is provided with thecylinder 127 for imparting rotation from a motor and a speed reducer(not shown) to the lower turn table and thrust bearings 130 that supportthe load of the turn tables. The lower turn table 123 is also equippedwith temperature regulating means (not shown) therein for controllingthe turn table temperature.

It is preferred that materials of the upper and lower turn tables 122and 123 be stainless steel (SUS), allowing easy deformation of the turntables with the shape adjustment means, etc. Although the polishing pads125 attached to the under surface of the upper turn table 122 and thetop surface of the lower turn table 123 are not limited, hardpolyurethane foam pads and soft non-woven cloth pads made by hardeningpolyurethane-resin-impregnated non-woven cloth, which are ordinarypolishing pads, are among usable pads as described above.

The slurry supply means 134 are constituted by providing slurry supplyholes on the upper turn table via a rotary joint (not shown) and canchange slurry supply amount, for example, by a solenoid valve that isnot shown and the like. A plurality of slurry supply means can beformed, and it is preferred that the slurry supply means be arrangedsuch that slurry is constantly supplied to the wafer surfaces.

In such the double-side polishing apparatus 121, it is preferred that aPCD of upper turn table load supporting points that is a diameter of acircle joining the load supporting points of the upper turn table 122coincide with a PCD of carrier plate centers that is a diameter of acircle joining the centers of the plurality of carrier plates 126.

More specifically, load supporting points of the upper turn table 122 inthe double-side polishing apparatus 121 are located on the fixing means129 that are joining portions between the upper turn table 122 and thehousing 128 as described above. Consequently, the PCD of upper turntable load supporting points can be expressed by the diameter of thecircle joining the centers of the fixing means 129 that are the loadsupporting points of the upper turn table. Since a plurality of waferholding holes are formed on the carrier plates 126 in the double-sidepolishing apparatus 121, it is difficult to cause the PCD of centers ofthe wafer holding holes that is the average diameter of the circlejoining the centers of wafer holding holes on the carrier plates 126 tocoincide with the PCD of upper turn table load supporting points. In thecase of the double-side polishing apparatus 121, for this reason, thePCD of carrier plate centers that is the diameter of the circle joiningthe centers of the plurality of carrier plates 126 is caused to coincidewith the PCD of upper turn table load supporting points. Thereby, it ispossible to improve responsiveness of turn table deformation (inparticular, linearity) to adjustments of slurry supply amount,adjustments of the shape adjustment means, etc. during wafer polishing,thus making the double-side polishing apparatus in which it is possibleto polish wafers stably while controlling wafer shape to be polishedwith high precision.

At this time, while a perfect coincidence is preferred between the PCDof upper turn table load supporting points and the PCD of carrier platecenters, it suffices to achieve a coincidence within a tolerance of 5 mmor less as mentioned earlier, improving responsiveness of turn tabledeformation to adjustment of polishing conditions. The present inventionincludes cases in which such a certain amount of tolerance exists.

Next, a method for simultaneously polishing both front and back surfacesof wafers will be demonstrated using the four-way double-side polishingapparatus shown in FIG. 11.

First, the wafers 124 are inserted into and held by the plurality ofcarrier plate 126 on which the wafer holding holes are formed. Then, thewafers 124 held by the carrier plates 126 are sandwiched by the upperand lower turn tables 122 and 123, to which the polishing pads 125 areattached, using an elevating device (not shown) for causing the upperand lower turn tables 122 and 123 to advance or retreat along therotational axis. Then, the upper turn table 122 is rotated by an upperrotation motor (not shown) via the cylinder 127 in a horizontal planeand the lower turn table 123 is rotated by a lower rotation motor (notshown) via the cylinder 127 in a horizontal plane while supplying slurryfrom the slurry supply means 134. By rotating and revolving theplurality of carrier plates 126 with the sun and internal gears 131 and132 concurrently with the rotation of the upper and lower turn tables122 and 123, it is possible to uniformly polish both front and backsurfaces of the wafers.

At this time, neither rotation speeds nor rotation directions of theupper and lower turn tables nor pressing forces applied to the wafers bythe upper and lower turn tables, etc. are limited, and polishing can becarried out in conventional polishing conditions.

By adjusting amount of slurry supplied from the slurry supply means 134during simultaneous polishing of both front and back surfaces of thewafers, it is possible to control polishing surface temperature, andthereby, the wafers can be polished stably without deteriorating wafershape while controlling the turn table shape with excellentresponsiveness. In this case, type of slurry used is not limited asmentioned earlier.

At this time, it is preferred that slurry supply amount be adjusted inaccordance with usage time of the polishing pads. This ensures goodprecision in the turn table shape control in accordance with changes inpolishing ability and other factors of polishing pads over time. Forinstance, it suffices to adjust slurry supply amount such that supplyamount is reduced over time with increasing usage time of the polishingpads, and the rate is set as appropriate according to the polishingapparatus and the polishing conditions used. Thus, by adjusting slurrysupply amount in accordance with usage time of the polishing pads, it ispossible to deform the turn table shape so as to compensate forvariations in wafer shape associated with progress of polishing, thusenabling polishing while easily controlling wafer shape. Further, evenduring polishing of a plurality of batches of the wafers, change inwafer shape over time can be suppressed and it is possible to polish thewafers stably while controlling wafer shape with good precision withoutdeteriorating wafer shape.

On the other hand, wafer polishing is conducted while controlling theturn table shape by providing the shape adjustment means 133 at loadsupporting point portions of the upper turn table 122 and adjusting theshape adjustment means 133 during simultaneous polishing of both frontand back surfaces of the wafers as described above. This makes itpossible to forcibly deform the upper turn table shape with the shapeadjustment means, for example, as shown in FIGS. 10( b) and 10(c). Byclarifying in advance a relationship between polishing conditions suchas polishing temperature and change in wafer shape and properlyadjusting the micrometers based on the relationship, it is possible todeform the turn table shape so as to compensate for variations in wafershape associated with progress of polishing, thus allowing polishingwhile easily controlling wafer shape. Further, even during polishing ofa plurality of batches of the wafers, change in wafer shape over timecan be suppressed and it is possible to polish the wafers stably whilecontrolling wafer shape with good precision without deteriorating wafershape.

Further at this time, it is preferred that the wafers be polished withcausing the PCD of upper turn table load supporting points that is thediameter of the circle joining the load supporting points of the upperturn table 122 and the PCD of carrier plate centers that is the diameterof the circle joining the centers of the plurality of carrier plates tocoincide with each other. Thus, by causing the PCD of upper turn tableload supporting points and the PCD of carrier plate centers to coincidewith each other, it is possible to improve responsiveness of the turntable shape control to adjustment of slurry supply amount and adjustmentof the shape adjustment means, thus ensuring high precision in the turntable shape control. Consequently, it becomes possible to preciselycontrol the turn table shape so as to compensate for variations overtime in wafer shape associated with progress of polishing, thus allowingpolishing while controlling wafer shape more easily. Thereby, it ispossible to maintain wafer shape with good precision and to performpolishing stably even during repeated polishing of a plurality ofbatches of wafers.

At this time, the responsiveness of turn table deformation to change in(adjustment of) slurry supply amount and adjustment of the shapeadjustment means is very good as with the double-side polishingapparatus 101. Consequently, it is possible to perform polishing stablywith high precision without deteriorating wafer shape, for example, byadjusting slurry supply amount or the shape adjustment means inconsideration of responsiveness of wafer shape (linearity) so as tocompensate for variations in wafer shape arising as a result ofcontinuous and repeated polishing with the same polishing pads.

Further, adjustment of slurry supply amount and the shape adjustmentmeans together and adjustment of both in conjunction with adjustment ofthe turn table temperature with the temperature regulating meansprovided in the turn table permit more precise and easy control in theturn table shape. This allows maintaining of batch-by-batch wafer shapewith extremely high precision and ensures stability in polishing evenduring repeated polishing of a plurality of batches of wafers.

It should be understood that the turn table shape control throughadjustment of slurry supply amount and adjustment of the shapeadjustment means may be conducted every polishing batch or in the middleof polishing as with the above.

The present invention will be explained more specifically as describedin the examples and comparative examples below, but the presentinvention is not limited thereto.

First, to evaluate responsiveness of turn table deformation according tochanges in polishing conditions when the wafer double-side polishingapparatus of the present invention and a conventional wafer double-sidepolishing apparatus are used, experiments were conducted in relation toresponsiveness of wafer shape, and particularly linearity.

EXAMPLE 1

A double-side polishing apparatus was used in which the PCD of upperturn table load supporting points and the PCD of centers of the waferholding holes on the carrier plate (centers of wafers held by thecarrier plate) were coincident at 600 mm and in which the carrier plateperformed a circular motion not accompanied by its rotation, with theaverage position of pitch circles formed by centers of wafer holdingholes on the carrier plate coincident with the position of pitch circleformed by load supporting points of the upper turn table duringpolishing, as shown in FIG. 1.

Using the double-side polishing apparatus, five silicon wafers havingdiameter of 300 mm (one batch) were first inserted into respective waferholding holes of the carrier plate (carrier plate having five waferholding holes) so as to be rotatable. Each wafer was pressed at 200g/cm² by the upper and lower turn tables to which soft non-woven cloths(polishing pads) were attached.

Then, the upper and lower turn tables were rotated, with the upper andlower polishing pads pressed against front and back surfaces of thewafers, and the timing chain was caused to perform an cyclic motionusing a circular motion motor while supplying slurry from the upper turntable side. This allowed each of the eccentric arms to rotate insynchronization in a horizontal plane, causing the carrier holdercoupled to each eccentric shaft and the carrier plate to perform acircular motion (circular motion of about 10 cm in diameter) notaccompanied by their rotation in a horizontal plane parallel to thesurface of the carrier plate, so that both front and back surfaces ofthe wafers were polished. Note that the slurry used was that in whichpolishing abrasive grain consisting of colloidal silica of 0.05 μm ingrain size was dispersed in alkali solution with pH 10.5.

In example 1, responsiveness of wafer shape was examined under varyingpolishing conditions during the above polishing process, by varying thecooling water temperature in the turn tables at equal intervals. Thechange in wafer shape (change in the turn table shape) to temperaturechange was actually confirmed by setting the cooling water temperatureto 22° C. in polishing condition 1 and increasing the temperature to 30°C. in steps of 2° C. (polishing conditions 1 to 5).

At this time, responsiveness of wafer shape to changes in polishingconditions was evaluated by measuring unevenness in wafers, asparameters representing wafer shape, and confirming thicknesses at thecenter and perimeter portions. Variations were relatively evaluated byusing the shape of experimental condition 3 as reference and treatingthe shapes more convex as positive and those more concave as negative.

COMPARATIVE EXAMPLE 1

For comparison, a conventional double-side polishing apparatus as shownin FIG. 5 was used in which the PCD of upper turn table load supportingpoints and the PCD of centers of the wafer holding holes on the carrierplate (centers of wafers held by the carrier plate) were respectivelyset to 600 mm and 640 mm and in which the carrier plate performed acircular motion not accompanied by its rotation to polish both front andback surfaces of the wafers. Wafers were polished under same conditionsas example 1 except for that (in particular, the polishing pads withsimilar usage times were used).

FIG. 6 shows evaluation results for responsiveness of wafer shape tochanges in polishing conditions in example 1 and comparative example 1.The results are plotting of average values of five wafers (one batch)for each polishing condition. It is apparent as shown in FIG. 6 thatexample 1 exhibits good linearity (correlation coefficient: 0.997) andgood responsiveness of wafer shape (that is, responsiveness of turntable deformation) to change in polishing condition. It is apparent thatthe comparative example exhibits poor and widely varying linearity(correlation coefficient: 0.898) and poor responsiveness.

As described above, the double-side polishing apparatus of the presentinvention provides good responsiveness of turn table deformation tochange in polishing condition. Therefore, it is possible to performpolishing stably with high precision without deteriorating wafer shape,for example, by controlling turn table temperature in consideration ofresponsiveness of wafer shape (linearity) shown in FIG. 6 so as tocompensate for variations in wafer shape arising as a result ofcontinuous and repeated polishing with the same polishing pads.

EXAMPLE 2 AND COMPARATIVE EXAMPLE 2

Twenty batches of wafers were polished using the same double-sidepolishing apparatuses as were used in example 1 and comparative example1.

Five silicon wafers having diameter of 300 mm (one batch) were insertedinto respective wafer holding holes of the carrier plate (carrier platehaving five wafer holding holes) so as to be rotatable. Each wafer waspolished with pressed at a pressing force of 200 g/cm² by the upper andlower turn tables, to which soft non-woven cloths (polishing pads) wereattached. The slurry used was that in which polishing abrasive grainconsisting of colloidal silica of 0.05 μm in grain size was dispersed inalkali solution with pH 10.5. At this time, the polishing pads werecontinuously used without replacement for repeated polishing.

In the present experiment (example 2 and comparative example 2), 20batches of wafers were polished while correcting change in wafer shapeby adjusting the turn table temperature under a given condition everypolishing of five batches using the temperature regulating means in theturn tables. Adjustment in every five batches was made under the sameconditions in both example 2 and comparative example 2.

After polishing, the shapes of the obtained wafers were evaluated basedon GBIR. GBIR (Global Back Ideal Range) is defined as margin betweenmaximum and minimum positional displacements relative to a referencesurface possessed in a wafer surface and is equivalent to TTV (TotalThickness Variation) that is a conventional and customary specification.In the present measurement, evaluation was conducted using acapacitance-type flatness measurement apparatus (AFS3220) made by ADECorporation. At this time, relative variations were plotted, with GBIRof the first batch used as reference. Measurement results are shown inFIG. 7.

In example 2, since the responsiveness of turn table deformation wasimproved as a result of use of the double-side polishing apparatus ofthe present invention as shown in FIG. 7, it was possible to controlwafer shape within a given range through adjustment every five batchesand maintain wafer shape within a range up to a control target value (acontrol upper limit) even in polishing of a plurality of batches ofwafers. In comparative example 2, however, wafer shape was not improvedto an anticipated shape despite adjustment every five batches under agiven condition. Instead, wafer shape deteriorated with repeatedpolishing and was changed out of the control target value (the controlupper limit). This was attributed to poor responsiveness of the turntable deformation that prevented correction to an anticipated shape.

EXAMPLE 3 AND COMPARATIVE EXAMPLE 3

Twenty batches of wafers were polished using the four-way double-sidepolishing apparatus as shown in FIG. 4 in which the PCD of upper turntable load supporting points and the PCD of carrier plate centers wereboth set to 800 mm (example 3). For comparison, twenty batches of waferswere polished using a conventional four-way double-side polishingapparatus in which the PCD of upper turn table load supporting pointsand the PCD of carrier plate centers were set respectively to 800 mm and850 mm (comparative example 3).

A total of 15 silicon wafers having diameter of 300 mm (one batch) wereinserted into three wafer holding holes formed on each of the fivecarrier plates. Each wafer was polished with pressed at a pressing forceof 200 g/cm² by the upper and lower turn tables, to which soft non-wovencloths (polishing pads) were attached. The slurry used was that in whichpolishing abrasive grain consisting of colloidal silica of 0.05 μm ingrain size was dispersed in alkali solution with pH 10.5. At this time,20 batches of wafers were polished without replacement of the polishingpads while correcting change in wafer shape by adjusting the turn tabletemperature under a given condition every five batches using thetemperature regulating means in the turn tables. Adjustment every fivebatches was made under the same conditions in both example 3 and andcomparative example 3. After polishing, the shapes of the obtainedwafers were evaluated based on GBIR. Relative variations were plotted,with GBIR of the first batch used as reference. Measurement results areshown in FIG. 8.

In example 3, since the responsiveness of turn table deformation wasimproved as a result of use of the double-side polishing apparatus ofthe present invention as shown in FIG. 8, it was possible to controlwafer shape within a given range through adjustment every five batchesand maintain wafer shape within a range up to a control target value (acontrol upper limit) even in polishing of a plurality of batches ofwafers. In comparative example 3, however, wafer shape was not improvedto an anticipated shape despite adjustment every five batches. Instead,wafer shape deteriorated with repeated polishing and was changed out ofthe control target value (the control upper limit).

EXAMPLE 4

Twenty batches of silicon wafers were repeatedly polished whilecontrolling the turn table shape through adjustment of slurry supplyamount using a wafer double-side polishing apparatus as shown in FIG. 9in which the PCD of upper turn table load supporting points and the PCDof centers of the wafer holding holes on the carrier plate (centers ofwafers held by the carrier plate) were both set to 600 mm and in whichthe carrier plate performed a circular motion not accompanied by itsrotation, with the average position of pitch circles formed by centersof wafer holding holes on the carrier plate coincident with the positionof pitch circle formed by load supporting points of the upper turn tableduring polishing.

Five silicon wafers having diameter of 300 mm (one batch) were insertedinto respective wafer holding holes of the carrier plate (carrier platehaving five wafer holding holes) so as to be rotatable. Each wafer waspressed at a pressing force of 200 g/cm² by the upper and lower turntables, to which soft non-woven cloths (polishing pads) were attached.The upper and lower turn tables were rotated on the rotational axis,with the carrier plate performing a circular motion not accompanied byits rotation, to polish the wafers. The slurry used was that in whichpolishing abrasive grain consisting of colloidal silica of 0.05 μm ingrain size was dispersed in alkali solution with pH 10.5. The initialslurry supply amount was set to 4.0 liters/min.

Twenty batches of wafers were repeatedly polished without replacement ofthe polishing pads while correcting change in wafer shape by reducingslurry supply amount by 0.2 liters/min every polishing of five batches.

After polishing, the shapes of the obtained wafers were evaluated basedon GBIR. GBIR (Global Back Ideal Range) is defined as margin betweenmaximum and minimum positional displacements relative to a referencesurface possessed in a wafer surface and is equivalent to TTV (TotalThickness Variation) that is a conventional and customary specification.In the present measurement, evaluation was conducted using acapacitance-type flatness measurement apparatus (AFS3220) made by ADECorporation. Relative variations were plotted, with GBIR of the firstbatch used as reference. Measurement results are shown in FIG. 14.

In example 4, it was possible to control wafer shape within a givenrange through adjustment of slurry supply amount and maintain wafershape within a range up to a control target value (a control upperlimit) even in polishing of a plurality of batches of wafers as shown inFIG. 14.

EXAMPLE 5 AND COMPARATIVE EXAMPLE 4

Next, one batch of silicon wafers having diameter of 300 mm werepolished using the same wafer double-side polishing apparatus as inexample 4 in which water controlled at 25° C. was supplied to piping inthe turn tables that was the temperature regulating means. Then, watertemperature was raised to 40° C. by flowing hot water into thetemperature regulating means in the turn tables for polishing of thenext batch of silicon wafers. At this time, the shapes of two types ofwafers were compared; one (example 5) polished through forcibledeformation of the upper turn table into the state shown in FIG. 10B byadjusting the shape adjustment means constituted by the micrometers inaccordance with change in turn table temperature and the other(comparative example 4) polished without using the shape adjustmentmeans.

As a result, the shape of the wafer of example 5 polished throughadjustment of the shape adjustment means under varying turn tabletemperatures was nearly the same as that of the wafers of the firstbatch polished with the turn table temperature set at 25° C. Thus, itwas possible to control wafer shape during polishing, even in the caseof substantial changes in polishing conditions such as turn tabletemperature, by adjusting the shape adjustment means provided in theupper turn table. By contrast, the wafer shape of comparative example 4,polished without using the shape adjustment means, was extremely convex.

EXAMPLE 6

Twenty batches of silicon wafers were repeatedly polished as example 6while controlling the turn table shape through adjustment of slurrysupply amount using a four-way wafer double-side polishing apparatus asshown in FIG. 11 in which the PCD of upper turn table load supportingpoints and the PCD of carrier plate centers were both set to 800 mm.

First, a total of 15 silicon wafers having diameter of 300 mm (onebatch) were inserted into three wafer holding holes formed on each ofthe five carrier plates. Each wafer was polished with pressed at apressing force of 200 g/cm² by the upper and lower turn tables, to whichsoft non-woven cloths (polishing pads) were attached. The slurry usedwas that in which polishing abrasive grain consisting of colloidalsilica of 0.05 μm in grain size was dispersed in alkali solution with pH10.5. The initial slurry supply amount was set to 5.0 liters/min. Inexample 6, twenty batches of wafers were repeatedly polished withoutreplacement of the polishing pads while correcting change in wafer shapeby reducing slurry supply amount by 0.2 liters/min every polishing offive batches.

After polishing, the shapes of the obtained wafer were evaluated basedon GBIR. Relative variations were plotted, with GBIR of the first batchused as reference. Measurement results are shown in FIG. 15.

In example 6, it was possible to control wafer shape within a givenrange through adjustment of slurry supply amount and maintain wafershape within a range up to a control target value (a control upperlimit) even in polishing of a plurality of batches of wafers as shown inFIG. 15.

EXAMPLE 7 AND COMPARATIVE EXAMPLE 5

Next, one batch of silicon wafers having diameter of 300 mm werepolished using the same wafer double-side polishing apparatus as inexample 6 with the temperature of the temperature regulating means inthe turn tables controlled at 25° C. Then, the temperature of thetemperature regulating means in the turn tables was raised to 40° C. forpolishing of the next batch of silicon wafers. At this time, the shapesof two types of wafers were compared; one (example 7) polished throughforcible deformation of the upper turn table shape into the state shownin FIG. 10B by adjusting the shape adjustment means constituted by themicrometers in accordance with change in turn table temperature and theother (comparative example 5) polished without using the shapeadjustment means.

As a result, the shape of the wafer of example 7 polished throughadjustment of the shape adjustment means under varying turn tabletemperatures was nearly the same as that of the wafers of the firstbatch polished with the turn table temperature set at 25° C. Thus, itwas possible to control wafer shape during polishing, even in the caseof substantial changes in polishing conditions such as turn tabletemperature, by adjusting the shape adjustment means provided in theupper turn table. By contrast, the wafer shape of comparative example 5,polished without using the shape adjustment means, was extremely convex.

The present invention is not limited to the embodiment described above.The above-described embodiment is a mere example, and those havingsubstantially the same structure as that described in the appendedclaims and providing the similar functions and advantages are includedin the scope of the present invention.

For example, while in the foregoing embodiment, a double-side polishingapparatus was shown in which the carrier plate performs a circularmotion not accompanied by a rotation of the carrier plate as an exampleof the double-side polishing apparatus of the present invention, itshould be borne in mind that the present invention is not limitedthereto and any other double-side polishing apparatuses with any type ofcarrier plate motion are acceptable as long as the carrier plate motionallows uniform polishing of wafers.

While unevenness in wafers was evaluated in the foregoing examples asparameters representing wafer shape, other qualities are alsoacceptable. Responsiveness of the turn table shape to control can beimproved by causing the PCD of upper turn table load supporting pointsand the average PCD of centers of wafers held by the carrier plate (thePCD of carrier plate centers in the case of a four-way double-sidepolishing apparatus) to coincide with each other, and any waferqualities can facilitate control as long as such qualities are affectedby the turn table shape.

It should be understood that while the examples were described herein byciting, as examples, double-side polishing apparatuses for polishingwafers having diameter of 300 mm, the present invention is not limitedthereto and applicable also to double-side polishing apparatuses forpolishing wafers having diameter of 200 mm or other diameters. It shouldalso be appreciated that the number of wafer holding holes formed on thecarrier plate is not particularly limited and that an arbitrary numberof holes such as three, five or seven, may be formed.

1. A wafer double-side polishing apparatus comprising: a carrier platehaving wafer holding holes, a center of each wafer holding hole disposedalong a first pitch circle having a first diameter; upper and lower turntables to which polishing pads are attached; and a slurry supply means;wherein: with wafers held in the wafer holding holes, the carrier platebeing moved between the upper and lower turn tables while supplyingslurry, to simultaneously polish both front and back surfaces of wafers;the upper turn table further comprising a plurality of devices forfixing the upper turn table to support, the fixing devices loadsupporting points forming disposed along a second pitch circle having asecond diameter equal to the first diameter, the load supporting pointsconfigured to receive and distribute applied force to the upper turntable; the lower turn table further comprising a plurality of bearingdevices forming load supporting points disposed along a third pitchcircle having a third diameter equal to the first diameter, the loadsupporting points configured to receive and distribute applied force tothe lower turn table.
 2. The wafer double-side polishing apparatusaccording to claim 1, wherein the motion of the carrier plate is acircular motion not accompanied by rotation of the carrier plate.
 3. Awafer double-side polishing method comprising: holding wafers on acarrier plate having wafer holding holes for holding wafers, a center ofeach wafer holding hole disposed along a first pitch circle having afirst diameter; and moving the carrier plate between upper and lowerturn tables to which polishing pads are attached, while supplyingslurry, to simultaneously polish both front and back surfaces of thewafers; wherein: the upper turn table further comprising a plurality ofdevices for fixing the upper turn table to a support, the fixing devicesforming load supporting points disposed along a second pitch circlehaving a second diameter equal to the first diameter, the loadsupporting points configured to receive and distribute applied force tothe upper turn table; the lower turn table further comprising aplurality of bearing devices forming load supporting points disposedalong a third pitch circle having a third diameter equal to the firstdiameter, the load supporting points configured to receive anddistribute applied force to the lower turn table; and the wafers arepolished while applying force to the load supporting points of the upperturn table and while applying force to the load supporting points of thelower turn table.
 4. The wafer double-side polishing method according toclaim 3, wherein the motion of the carrier plate is a circular motionnot accompanied by rotation of the carrier plate.
 5. The waferdouble-side polishing method according to claim 3, wherein during thewafer polishing, the wafers are polished while controlling polishingconditions.
 6. The wafer double-side polishing method according to claim5, wherein the polishing condition control is performed by controllingthe temperature of the upper turn table and/or the lower turn table. 7.The wafer double-side polishing method according to claim 1, wherein:the bearing devices are thrust bearings.
 8. The wafer double-sidepolishing method according to claim 3, wherein: the bearing devices arethrust bearings.